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U  from VOA Special English Word Book

under - prep. below; below the surface of; less than; as called for by a law, agreement or system ("The river flows under the bridge." "Such action is not permitted under the law.")
understand - v. to know what is meant; to have knowledge of
unite - v. to join together
universe - n. all of space, including planets and stars
university - n. a place of education that usually includes several colleges and research organizations
unless - conj. except if it happens; on condition that ("I will not go, unless the rain stops.")
until - conj. up to a time; before
up - ad. to, in or at a higher position or value
urge - v. to advise strongly; to make a great effort to get someone to do something
urgent - ad. needing an immediate decision or action
us - pro. the form of the word "we" used after a preposition ("He said he would write to us.") or used as an object of a verb ("They saw us yesterday.")
use - v. to employ for a purpose; to put into action
usual - ad. as is normal or common; as is most often done, seen or heard