uncompromising.adjective
unwilling to grant concessions or negotiate; inflexible (the corporation took an uncompromising stance during negotiations with the union representing employee rights and benefits); displayed uncompromising honesty
uncompromisingly.adverb

ulterior.adjective
lying beyond what is evident, revealed or avowed, especially being concealed.intentionally so as to deceive (an ulterior motive); if you say that someone has an ulterior motive for doing something, you believe that they have a hidden reason for doing it (she had an ulterior motive for trying to help, that of her aspiration to become a nurse); lying beyond or outside the area of immediate interest; occurring later; subsequent; on the other side
ulteriorly.adverb

upbraid, upbraided, upbraiding, upbraids.transitive verbs
to reprove sharply; to get after; reproach; scold; upbraid generally suggests a well founded reproach, as one leveled by an authority (upbraided him for not having worn his overcoat out in the cold); if you upbraid someone, you tell them that they have done something.wrong and criticize them for doing it
upbraidingly.adverb
upbraider.noun,.plural.upbraiders

unduly.adverb
excessively; immoderately (unduly familiar with strangers)

unsubstantial.adjective
lacking.material.substance; insubstantial; lacking firmness or strength; flimsy; lacking basis in fact
unsubstantially.adverb
unsubstantiality.noun
unsubstantiated.adjective
a claim, accusation or story that is unsubstantiated has not been proved to be valid or true (unsubstantiated rumours about his private life; I do object to their claim, which I find totally unsubstantiated)

underpin, underpinned, underpinning, underpins.transitive verbs
to give support or substance to; to support from below, as with props, girders or masonry

unprecedented.adjective
having no previous example (unprecedented economic growth)
unprecedentedly.adverb

unction.noun,.plural.unctions
the act of anointing; an ointment or oil; a salve; something that serves to soothe; a balm; from Middle English meaning to anoint

unctuous.adjective
characterized by affected, exaggerated.or.insincere.earnestness; smarmy; having the quality or characteristics of oil or ointment; slippery; containing or composed of oil or fat
unctuously.adverb
unctuousness or unctuosity.noun

unwary, unwarier, unwariest.adjectives
not alert to deception or danger; not on the qui vive
unwarily.adverb
unwariness.noun

unbecoming.adjective
not appropriate, attractive or flattering (an unbecoming dress); not in accord with the standards implied by one's character or position (conduct unbecoming women of her caliber); improper
unbecomingly.adverb
unbecomingness.noun

unable.adjective
lacking the necessary power, authority or means; not able; incapable (unable to get to that town without a vehicle); lacking mental or physical capability or efficiency; incompetent (unable to do advanced mathematics)

unalienable.adjective
not to be separated, given away or taken away; not transferable to the ownership of another inalienable.(inalienable or unalienable rights); immutable; you have no rights until you learn to stand for them

umbrage.noun,.plural.umbrages
offense; resentment (took umbrage at their rudeness); something that affords shade; shadow or shad; a vague or indistinct indication; a hint of shadow or darkness; Note: umbrage is often followed by at (took umbrage at the comment; I imagine some people will take umbrage {=will be offended} when they hear the quote; example, I take umbrage at {=I am offended by} that remark)

unnerve, unnerved, unnerving, unnerves.transitive verbs
to deprive of fortitude, strength or firmness of purpose; to make nervous or upset
unnervingly.adverb

unimaginative.adjective
not using imagination; seemingly.unable to think of new methods or things to do

unimaginable.adjective
if you describe something as unimaginable, you are emphasizing that it is difficult, even almost impossible to imagine or begin to understand properly, because it is not part of a normal experience such as we have been used to (the scale of the universe is unimaginable); unbelievable; not possible to imagine or comprehend
unimaginably.adverb

unpremeditated.adjective
not planned or thought out in advance; extemporaneous
unpremeditatedly.adverb
compare premeditated

unsteady, unsteadier, unsteadiest.adjectives
not firm, solid or securely in place; unstable; marked.by.fluctuation or changeableness; inconstant (unsteady weather); wavering (an unsteady voice due to nervousness)
unsteady, unsteadied, unsteadying, unsteadies.transitive verbs
to cause to become unsteady
unsteadily.adverb
unsteadiness.noun.(words ending in 'ess' are usually without pluralization - adding an 'es' making '...esses' is clumsy)

unstable, unstabler, unstablest.adjectives
tending strongly to change (unstable weather); lacking control of one's emotions; not constant; fluctuating.(unstable vital signs); fickle; characterized by unpredictable behavior; not firmly placed; unsteady (an unstable ladder)
unstableness.noun.(words ending in 'ess' are usually without pluralization - adding an 'es' making '...esses' is clumsy)
unstably.adverb
Chemistry:.decomposing.readily
Physics:.decaying with relatively short lifetime; used of subatomic.particles; radioactive

usher.noun,.plural.ushers
one who is employed to escort people to their seats, as in a wedding, theater, church or stadium
usher, ushered, ushering, ushers.intransitive verbs
to serve as an usher (ushered every Sunday at church)

usher, ushered, ushering, ushers.verbs
transitive verb use.to precede and introduce (I'll usher on ahead and be ready to introduce you all when you arrive); to lead or conduct; guide; inaugurate; to serve as an usher to

upper hand
a position of control or advantage

unite, united, uniting, unites.verbs
transitive verb use.to bring together so as to form a whole; to combine people in interest, attitude or action (love unites humanity); to join a couple in marriage; to cause to adhere; to join and act together in a common purpose or endeavor; join; to be or become bound together by adhesion

unity.noun,.plural.unities
the state or quality of being one; a unit; singleness; the state or quality of being in accord; harmony; the combination or arrangement of parts into a whole; unification; a combination or union thus formed; singleness or constancy of purpose or action

unify, unified, unifying, unifies.transitive and intransitive verbs
to make into or become a unit; consolidate
unifiable.adjective
unification.noun,.plural.unifications
unifier.noun,.plural.unifiers

union.noun,.plural.unions
the act of uniting or the state of being united; a combination so formed, especially an alliance or confederation of people, parties for mutual interest or benefit; unity; a labor union; a student union
union.adjective

uniformitarianism.noun
the theory that all geologic.phenomena may be explained as the result of existing forces having operated uniformly from the origin of the Earth to the present time
uniformitarian.adjective & noun

uniform.adjective
always the same, as in character or degree; unvarying; conforming to one principle, standard or rule; consistent; being the same as or consonant with another or others; unvaried in texture, color or design; steady
uniform.noun,.plural.uniforms
one form; a distinctive outfit intended to identify those who wear it as members of a specific group; one set of such an outfit uniform, uniformed, uniforming, uniforms.transitive verbs
to make something uniform; to provide or dress with a uniform
uniformity.or.uniformness.noun
uniformly.adverb

undeceive, undeceived, undeceiving, undeceives.transitive verbs
to free from illusion or deception
undeceivably.adverb
undeceivable.adjective

unillumined.adjective
not illumined

unfavorable.adjective
not favorable; likely to be a hindrance; disadvantageous (unfavorable winds); having or showing opposition; adverse (an unfavorable reaction to vaccinations)
unfavorably.adverb
unfavorableness.noun

unwieldy, unwieldier, unwieldiest.adjectives
difficult to carry or manage because of bulk or shape (an unwieldy parcel); clumsy; ungainly
unwieldily.adverb
unwieldiness.noun

ungainly, ungainlier, ungainliest.adjectives
lacking grace or ease of movement or form; clumsy; awkward; difficult to move or use; unwieldy
ungainliness.noun

unweaned.adjective
a baby getting nourishment from its mother; not weaned yet

upstanding.adjective
morally upright; honest; doing the best one knows how to in standing up for what's right and good; standing erect or upright upstandingness.noun

uneasy, uneasier, uneasiest.adjectives
lacking a sense of security; anxious or apprehensive (the farmers were uneasy until it finally rained); affording no ease or reassurance (an uneasy calm occurs in the centre of a hurricane); awkward or unsure in manner; constrained (uneasy with strangers); causing constraint or awkwardness (an uneasy silence); not conducive to peace (allowed his mind to run all over the place with his thoughts)
unease.or.uneasiness.noun
uneasily.adverb

unimpeded.adjective
if something moves or happens unimpeded, it continues without being stopped or interrupted by anything; not impeded

unrequited.adjective
not reciprocated or returned in kind (unrequited love; an unrequited gift, not even a thank you)
unrequitedly.adverb

unadulterated.adjective
mot mingled or diluted with extraneous.matter; pure