When someone says something is monkey business it means silly, mischievous, or deceitful acts or behaviour.
Suspect, dishonest, or meddlesome behaviour or acts.
Improper or underhanded conduct; trickery.
1. Those group of men are up to monkey business.
2. Cops can tell if there is monkey business going on by the body language of criminals.
3. The 6th grade teacher warned us not to get into any monkey business while she went out to talk to a student.
4. There are rumours that the old factory was into monkey business.
absurdity, absurdness, antics, buffoonery, carrying-on, clowning around, craziness, disobedience, foolery, foolishness, hanky-panky, high jinks, hokey-pokey, horse feathers, horseplay, inanity, insanity, irresponsibility, ludicrousness, lunacy, misbehaviour, mischief, mischief-making, monkeyshine, nonsense, poppycock, prank, silliness, stupidity, tommyrot