undulate, undulated, undulating, undulates.verbs
transitive verb use.to cause to move in a smooth wavelike motion; to give a wavelike appearance or form to
intransitive verb use.to move in waves or with a smooth, wavelike motion; swing; to have a wavelike appearance or form; to increase and decrease in volume or pitch as if in waves
undulate, undulatory.adjectives
having a wavy outline or appearance (leaves with undulate margins)

undulation.noun
a regular rising and falling or movement to alternating sides; movement in waves; a wave like form, outline, or appearance; one of a series of waves or wavelike segments

unsound, unsoundest, unsounder.adjectives
not dependably strong or solid; not physically or mentally healthy; not true or logically valid; fallacious – an unsound conclusion
unsoundly.adverb
unsoundness.noun

ubiquitous.adjective
being or seeming to be everywhere at the same time; omnipresent
ubiquitously.adverb
ubiquitousness.noun

unanimous.adjective
based on or characterized by complete assent or agreement; sharing the same opinions or views; being in complete harmony or accord
unanimously.adverb
unanimousness, unanimity.nouns
the condition of being unanimous

uncouth.adjective
crude; unrefined; awkward or clumsy; not graceful
uncouthly.adverb
uncouthness.noun

unfathomable.adjective
difficult or impossible to understand; incomprehensible.(unfathomable theories); difficult or impossible to measure (the unfathomable depths)

ultraviolet.adjective
of or relating to the range of invisible radiation wavelengths from about 4 nanometers, on the border of the x-ray region, to about 380 nanometers, just beyond the violet in the visible spectrum
ultraviolet.noun
ultraviolet light or the ultraviolet part of the spectrum

uncertainty principle.noun
a principle in quantum mechanics formulated in 1927 by the German physicist Werner Heisenberg holding that increasing the accuracy of measurement of one observable quantity increases the uncertainty with which other quantities may be known

understate, understated, understating, understates.verbs
transitive verb use.to state with less completeness or truth than seems warranted by the facts; to express with restraint or lack of emphasis, especially ironically or for rhetorical effect; to state (a quantity, for example) that is too low  (understate corporate financial worth)
intransitive verb use.to give an understatement

Ur.noun
the port of Babylonia, whence trade was carried on with the dwellers on the gulf, and with the distant countries of India, Ethiopia, and Egypt. It was abandoned about 500 B.C., but continued to be a great sacred cemetery city, as is evident from the number of tombs found there.

umpteen, umpteenth.adjectives
relatively large but unspecified in number (umpteen reasons; umpteen guests)

upwell, upwelled, upwelling, upwells.intransitive verbs
to rise from a lower or inner source; well up
upwelling.noun
the act or an instance of rising up from or as if from a lower source (an upwelling of emotion); a process in which cold, often nutrient rich waters from the ocean depths rise to the surface

uric acid.noun
a semisolid compound, C₅H₄N₄O₃-(5 parts {molecules}-carbon, 4 parts hydrogen, 4 parts nitrogen, 3 parts oxygen) that is a nitrogenous end product of protein and purine-metabolism.

unbeknownst, unbeknown.adjectives
occurring or existing without the knowledge of; unknown
unbeknownst.adverb
without the knowledge of a specified party

utilitarianism.noun
the belief that the value of a thing or an action is determined by its utility; the ethical theory proposed by Jeremy Bentham and James Mill that all action should be directed toward achieving the greatest happiness for the greatest number of people

utilitarian.adjective
of, relating to, or in the interests of utility (utilitarian considerations in industrial design); exhibiting or stressing utility over other values; practical (plain, utilitarian kitchenware); of, characterized by, or advocating utilitarianism
utilitarian.noun
one who advocates or practices utilitarianism

unwitting.adjective
not knowing; unaware (an unwitting subject in an experiment); not intended; unintentional (an unwitting admission of guilt)
unwittingly.adverb

unsophisticated.adjective
not sophisticated; naive
unsophisticatedly.adverb
unsophisticatedness, unsophistication.nouns

uphold, upheld, upholding, upholds.transitive verbs
to hold aloft; raise: upheld the banner proudly; to prevent from falling or sinking; support; to maintain or affirm against opposition
upholder.noun

unseemly, unseemlier, unseemliest.adjectives
not in accord with accepted standards of good taste; grossly improper; not suited to the circumstances; inappropriate
unseemly.adverb
in an improper or inappropriate manner
unseemliness.noun

understanding.noun
the quality or condition of one who understands; comprehension; the faculty by which one understands; intelligence; reason; individual or specified judgment or outlook; opinion. 4.a. A compact.implicit between two or more people or groups; the matter implicit in such a compact; a reconciliation of differences; a state of agreement (they finally reached an understanding); a disposition to appreciate or share the feelings and thoughts of others; sympathy
understanding.adjective
characterized by or having comprehension, good sense, or discernment; compassionate; sympathetic
understandingly.adverb
understand, understood, understanding, understands.transitive verbs
to perceive and comprehend the nature and significance of; grasp; apprehend; to know thoroughly by close contact or long experience with (that teacher understands children fairly well); to grasp or comprehend the meaning intended or expressed (they have trouble with English, but I can understand them; to know and be tolerant or sympathetic toward (I can understand your point of view even though I disagree with it); to learn indirectly, as by hearsay.(I understand his departure was unexpected)
intransitive use.to have understanding, knowledge, or comprehension; to have sympathy or tolerance; to learn something indirectly or secondhand; gather.
understandability.noun
understandable.adjective
understandably.adverb

unintelligible.adjective
being such that understanding or comprehension is difficult or impossible; incomprehensible.(unintelligible remarks; an unintelligible prose passage)
unintelligibility or unintelligibleness.noun
unintelligibly.adverb

unkempt.adjective
not combed (unkempt hair); not properly maintained; disorderly or untidy (an unkempt garden); sloppy; unpolished; rude

undercurrent.noun
an underlying tendency, force, or influence often contrary to what is superficially evident; an intimation; a current, as of air or water, below another current or beneath a surface