1520s, likely from an unrecorded Middle Low German *moneke or Middle Dutch *monnekijn, a colloquial word for "monkey," originally a diminutive of some Romanic word, cf. French monne (16c.); Middle Italian monnicchio, from Old Italian monna; Spanish mona "ape, monkey." In a 1498 Low German version of the popular medieval beast story "Roman de Renart" ("Reynard the Fox"), Moneke is the name given to the son of Martin the Ape; transmission of the word to English might have been via itinerant entertainers from the German states.
The Old French form of the name is Monequin (recorded as Monnekin in a 14c. version from Hainault), which could be a diminutive of some personal name, or it could be from the general Romanic word, which may be ultimately from Arabic maimun "monkey," literally "auspicious," a euphemistic usage because the sight of apes was held by the Arabs to be unlucky [Klein]. The word would have been influenced in Italian by folk etymology from monna "woman," a contraction of ma donna "my lady."
Monkey has been used affectionately for "child" since c.1600. As a type of modern popular dance, it is attested from 1964. Monkey business attested from 1883. Monkey suit "fancy uniform" is from 1886. Monkey wrench is attested from 1858; its figurative sense of "something that obstructs operations" is from the notion of one getting jammed in the gears of machinery (cf. spanner in the works). To make a monkey of someone is attested from 1900. To have a monkey on one's back "be addicted" is 1930s narcotics slang, though the same phrase in the 1860s meant "to be angry." There is a story in the Sinbad cycle about a tormenting ape-like creature that mounts a man's shoulders and won't get off, which may be the root of the term. In 1890s British slang, to have a monkey up the chimney meant "to have a mortgage on one's house." The three wise monkeys ("see no evil," etc.) are attested from 1926.