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umbilical cord a cord that connects an unborn baby to its mother. The umbilical cord supplies nourishment to the fetus and takes away wastes.
umbrella a screen made of fabric stretched over a folding frame. An umbrella is used to shield against the rain or sun.
umpire a person who rules on plays in a game; referee. [2 definitions]
UN an abbreviation for United Nations.
un- a prefix that means "not." [2 definitions]
unable not having the power, skill, or means needed to do something; not able.
unanimous in complete agreement. [2 definitions]
unaware not aware; not realizing. [2 definitions]
unawares by surprise or in a way that was not expected.
unbeaten not defeated or outdone. [2 definitions]
unbecoming not attractive or proper on a particular person. [2 definitions]
unbelievable astounding or very hard to believe.
uncanny beyond ordinary human or natural means or ability.
uncertain not known for sure; not definite. [3 definitions]
uncle the brother or brother-in-law of one's father or mother. [2 definitions]
unclear hard to understand; confusing. [2 definitions]
Uncle Sam a cartoon person that represents the government or people of the United States. Uncle Sam is a tall, thin man with a beard, top hat, and trousers that have red and white stripes. [2 definitions]
uncomfortable feeling discomfort; not comfortable. [2 definitions]
uncommon unusual or rare.
unconscious not conscious or aware. [3 definitions]
unconstitutional not according to the constitution of a state or country.