also rat's-tail, used since 16c. of conditions or devices held to resemble a rat's long, hairless tail in some sense, including "lank lock of hair" (1810); "end of a rope" (1867); from rat (n.) + tail (n.1).
rat-pack
rat-poison
rat-race
rats
ratsbane
rat-tail
rattan
rattle
rattler
rattlesnake
rattletrap