means A tradesperson who makes, fits, repairs, and picks locks and keys — and who can let you back into your own home or car when you're locked out.

from A plain compound, as honest as the trade: "lock" plus "smith." The first comes from Old English loc, a fastening or bolt, kin to words meaning to close or shut. The second, smith, is the ancient word for a metalworker — one who strikes and shapes metal, the same root that gives us blacksmith and goldsmith and the surname Smith. So a locksmith is, quite literally, a smith of locks: a metalworker who forged the cleverest little prisons for keys.