cat
In addition to the idioms beginning with cat, also see alley cat; bell the cat; curiosity killed the cat; fat cat; grin like a Cheshire cat; let the cat out of the bag; like a cat on a hot brick; look like something the cat dragged in; look like the cat that ate the canary; more than one way to skin a cat; not enough room to swing a cat; play cat and mouse; rain cats and dogs; when the cat's away.