Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
also double-entendre, 1670s, from French (where it was rare and is now obsolete), literally "a twofold meaning," from entendre (now entente) "to hear, to understand, to mean," from Latin intendere (see intend). The proper Modern French phrase would be double entente, but the phrase has become established in English in its old form.
Wiktionary
n. 1 (context idiomatic English) A phrase that has two meanings, especially where one is innocent and literal, the other risqué, bawdy, or ironic; an innuendo. 2 (context nonstandard English) (double entendre English)Category:English plurals
WordNet
n. an ambiguity with one interpretation that is indelicate
Wikipedia
A double entendre (; ) is a figure of speech or a particular way of wording that is devised to be understood in either of two ways, having a double meaning. Typically one of the meanings is obvious, given the context whereas the other may require more thought. The innuendo may convey a message that would be socially awkward, sexually suggestive or offensive to state directly (the Oxford English Dictionary describes a double entendre as being used to "convey an indelicate meaning", whilst Longman Dictionary of Contemporary English defines it as "a word or phrase that may be understood in two different ways, one of which is often sexual").
A double entendre may exploit puns to convey the second meaning. Double entendres generally rely on multiple meanings of words, or different interpretations of the same primary meaning. They often exploit ambiguity and may be used to introduce it deliberately in a text. Sometimes a homophone (i.e., another word which sounds the same) can be used as a pun. When three or more meanings have been constructed, this is known as a "triple entendre", etc.
Usage examples of "double entendre".
It was Rosetti who suggested they go upstairs, without any awkwardness or connived double entendre, escorting her to her door with the promise to see her for breakfast and moving on to his own room the moment she turned the key in the lock.
Foresightfully, von Mannheim had left Germany in good time, but he started over in Hollywood at the bottom (forgive the double entendre).
There often lurks behind my words some double entendre which you may not understand, perhaps until much later.