the.com/key chain

means A small ring or clip used to hold keys together so they're easier to carry and less likely to be lost individually.

from Straightforward compound: 'key,' from Old English 'cæg' (origin itself obscure, no solid cognates elsewhere, oddly enough for such an old everyday object), plus 'chain,' from Old French 'chaine,' tracing back to Latin 'catena' meaning a connected series of links. The device itself — a simple ring or linked chain for grouping keys — likely became common as people started carrying multiple keys regularly, once locks multiplied with urban life, doors, cabinets, vehicles. No dramatic invention story here: just practical hardware catching up to the practical problem of pockets full of loose metal.