"Monkey business" as a phrase is the story of compounding the vernacular with etymology. The verb "monkey" is typically used in informal speech to indicate immature, inappropriate, or uncouth behavior -- as in "Stop monkeying around!" Similarly, the adjective form of "monkey" operates as a descriptive modifier indicating a general lack of seriousness. Hence, "monkey business" indicates business which is not serious.

The second part of this compound phrase, "business," is best exemplified through some brief etymology. The root of business is "busy," as in "busy-ness." Meaningless business is often referred to as busy work to separate important busy-ness from unimportant busy-ness.

In the phrase "monkey business," the more vulgar etymology of the word business is emphasized, as one cannot be serious about non-serious matters. In this manner, the phrase "monkey business" combines slang terminology with some of the history of the word business to denote "silly busy work".

A number of films, mostly comedies, have been made with the title Monkey Business, notably by the Marx Brothers in 1931 and by Howard Hawks in 1952.