| 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 |
abbreviation of "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 knowing or realizing; not conscious of. [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. |