If there is not enough room to swing a cat, it means that there is a lack of room in a given area.
This expression is often thought to be related not to live cats, but a cat o'nine tails - a vicious type of whip, typically used to discipline sailors.
Boats aren't known for being roomy, and a sailor complaining about living in close quarters might be heard to remark "Shiver me timbers! There's not room to swing a cat in here. Aar." Or something of the sort.
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Very little space, cramped quarters, as in There's not enough room to swing a cat in this tent. This expression, first recorded in 1771, is thought to allude to the cat-o'-nine-tails, or "cat," a whip with nine lashes widely used to punish offenders in the British military.