[ugly duckling] {n.} An ugly or plain child who grows up […]

[uh-huh] or [um-hum] {adv.}, {informal} Yes. - Used only in speech […]

[ul] Unlucky (gaming term)

[UL, U/L] "Upload"; sending data to a remote host.

[um-hum] See: [UH-HUH].

[Umfriend] One with whom one has a sexual relationship; as in: […]

[unbosom oneself] {v. phr.} To confess one's personal thoughts or feelings; […]

[uncertain] See: [IN SO MANY WORDS] (2) or [IN NO UNCERTAIN […]

[uncle] See: [SAY UNCLE] also [CRY UNCLE].

[under] See: [CUT THE GROUND FROM UNDER], [GO UNDER], [OUT FROM […]