Monkey (noun)

1. A small to medium-sized primate that typically has a long tail, most kinds of which are arboreal.
2. An ape or monkey used in laboratory research.
3. A person who is regarded as frivolous, impish, or mischievous.
4. A person who is easily deceived or tricked.
5. A person who is not serious or reliable.

Origin:

Middle english: from old english moncyn, of west germanic origin; related to dutch monekijn and german affe, also to ape.

Examples:

1. The monkey in the zoo.
2. The laboratory monkey.
3. The monkey around the party.
4. The monkey of the class.
5. The monkey of the business.