Definition -
(1) An ambiguously structured clause or sentence that can be interpretted in multiple ways.
(2) A figure of speech where the ambiguity is purposely created by using an ambiguously structured clause or sentence.

Example -
"I once shot an elephant in my pajamas. How he got in my pajamas I'll never know."
(Groucho Marx, Animal Crackers)

Etymology -
The word derives from the Greek amphibolia, ambiguity + logia, speech.

Oxford English Dictionary -
Its first citation for sense (1) is from circa 1374:
"For goddes speken in amphibologies, And for o soth, they tellen twenty lyes."
(Chaucer Troylus iv. 1406)

Its first citation in sense (2) is from 1589:
"Such ambiguous termes they call Amphibologia, we call it the ambiguous, or figure of sence incertaine."
(Puttenham Eng. Poesie (Arb.) 267)

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