means A framework of bars, shelves, or pegs for holding or storing things — though the same word also names a medieval torture device that stretched the body, a horse's gait, and the act of straining or tormenting (as in 'rack your brain').

from From Middle Dutch or Middle Low German 'rec' or 'recke,' meaning a framework or bar, related to a Germanic root for 'to stretch' (a cousin of 'reach'). That stretching sense is the dark thread connecting the storage frame to the torture engine — both involve things pulled taut over a structure. The phrase 'rack one's brains' borrows this image of straining painfully, while 'rack and ruin' is actually a different word, an old variant of 'wrack' (wreckage), often confused with this one.