Is lock a noun

Yes, the Word 'lock' is both a noun (lock, locks) and a verb (lock, locks, locking, locked).

The noun 'lock' is a Word for a device to secure something from opening or being moved; a Word for a clump of hair; a Word for a thing.

The Word 'lock' means to secure something with a device to prevent opening or moving; to become stuck in place preventing movement.