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vulgar, crass, debauch or low; often of a sexual intonation or nature.
A lude gesture or display.

This term is used often but does not appear in dictionaries, while Definition 1 (Quaalude) appears in most dictionaries but is rarely used.
by Person Anonymous June 01, 2005
Not merely an abbreviation, this term can be used to denote poor, socially unacceptable behavior.
"His behavior at dinner was crass and lude."

"He was making lude gestures."
by Fox April 15, 2005