Pun

[puhn] /pʌn/

noun
1.
the humorous use of a word or phrase so as to emphasize or suggest its different meanings or applications, or the use of words that are alike or nearly alike in sound but different in meaning; a play on words.
2.
the word or phrase used in this way.
verb (used without object), punned, punning.
3.
to make puns.
/pʌn/
noun
1.
the use of words or phrases to exploit ambiguities and innuendoes in their meaning, usually for humorous effect; a play on words. An example is: “Ben Battle was a soldier bold, And used to war’s alarms: But a cannonball took off his legs, So he laid down his arms.” (Thomas Hood)
verb puns, punning, punned
2.
(intransitive) to make puns
/pʌn/
verb puns, punning, punned
1.
(transitive) (Brit) to pack (earth, rubble, etc) by pounding
n.

1660s (first attested in Dryden), of uncertain origin, perhaps from pundigron, which is perhaps a humorous alteration of Italian puntiglio “equivocation, trivial objection,” diminutive of Latin punctum “point.” This is pure speculation. The verb also is attested from 1660s. Related: Punned; punning.

Pun was prob. one of the clipped words, such as cit, mob, nob, snob, which came into fashionable slang at or after the Restoration. [OED]

A humorous substitution of words that are alike in sound but different in meaning (see double-entendre), as in this passage from Alice’s Adventures in Wonderland, by Lewis Carroll:

“And how many hours a day did you do lessons?” said Alice, in a hurry to change the subject.
“Ten hours the first day,” said the Mock Turtle, “nine the next, and so on.”
“What a curious plan!” exclaimed Alice.
“That’s the reason they’re called lessons,” the Gryphon remarked: “because they lessen from day to day.”