monkey

monkey a monkey is proverbially taken as the type of a clever, artful, or amusing person. Monkeys were often in the past kept as domestic pets, and proprietors of barrel-organs were typically accompanied by a monkey, giving rise to an extended metaphor in which the monkey stands for the junior member of a disparaged partnership (see organ-grinder).

Recorded from the mid 16th century, the word is of unknown origin, perhaps from Low German; in the Middle Low German version of Reynard the Fox (1498), Moneke appears once as the name of the son of Martin the Ape.
as artful as a wagonload of monkeys extremely clever or mischievous.
monkey business mischievous or deceitful behaviour.
a monkey on one's back a burdensome problem.
Monkey Trial a trial of a teacher for teaching evolutionary theories, contrary to the laws of certain States of the US, specifically that of J. T. Scopes in Dayton, Tennessee (10–21 July, 1925), with William Jennings Bryan for the prosecution, and Clarence Darrow for the defence. Scopes was convicted, and fined $100 dollars.
three wise monkeys a conventional sculptured group of three monkeys; used allusively to refer to a person who chooses to ignore or keep silent about wrongdoing. One monkey is depicted with its paws over its mouth (taken as connoting ‘speak no evil’), one with its paws over its eyes (‘see no evil’), and one with its paws over its ears (‘hear no evil’).

See also cold enough to freeze the balls off a brass monkey, if you pay peanuts, you get monkeys.