Another word for key
Instrument to open a lock
latchkey, opener, master key, passkey, skeleton key, passe-partout (French).
A means of solution
answer, explanation, solution, clue, index, pointer, pivot, hinge, crux, fulcrum, lever, nexus, core, root, taproot, nucleus, earmark, marker, symptom, sign, brand, cipher, code, indicator, blueprint, signboard, tip-off*; see also answer 2.
Another word for keynoun
A means or method of entering into or achieving something desirable:formula, route, secret. (Informal) ticket. See means