joke

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Something said or done to evoke laughter or amusement, especially an amusing story with a punch line.
• noun A mischievous trick; a prank.
• noun Something that is of ludicrously poor quality.
• noun Something not to be taken seriously; a triviality.
• noun An object of amusement or laughter; a laughingstock.
• intransitive verb To tell or play jokes; jest.
• intransitive verb To speak in fun; be facetious.
• intransitive verb To say or write as a joke.

from The Century Dictionary.

• To jest; make merry about something.
• To cast jokes at; make merry with; rally: as, to joke a man about his love-affairs.
• noun Something said or done for the sake of exciting laughter; some witty or sportive remark or act; a jest; also, jesting; raillery.
• noun Something not real, or to no purpose; what is not in earnest or actually meant; an illusion.
• noun Synonyms See jest.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To make merry with; to make jokes upon; to rally; to banter.
• noun Something said for the sake of exciting a laugh; something witty or sportive (commonly indicating more of hilarity or humor than jest); a jest; a witticism.
• noun Something not said seriously, or not actually meant; something done in sport.
• noun in jest; sportively; not meant seriously.
• noun See under Practical.
• intransitive verb To do something for sport, or as a joke; to be merry in words or actions; to jest.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An amusing story.
• noun Something said or done for amusement.
• noun figuratively The root cause or main issue, especially an unexpected one
• noun figuratively A worthless thing or person.
• verb intransitive To do or say something for humourous amusement rather than seriously.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a triviality not to be taken seriously
• noun a humorous anecdote or remark intended to provoke laughter
• noun a ludicrous or grotesque act done for fun and amusement
• verb tell a joke; speak humorously
• verb act in a funny or teasing way
• noun activity characterized by good humor