How to sign: metal device shaped in such a way that when it is inserted into the appropriate lock the lock's mechanism can be rotated
Categories: device
Within this category: ignition key, latchkey, passkey
How to sign: serving as an essential component
"a cardinal rule"; "the central cause of the problem"; "an example that was fundamental to the argument"; "computers are fundamental to modern industrial structure";
Similiar / Same: cardinal, central, fundamental, primal