Indispensable, supremely important. / Important, salient.

To fit (a lock) with a key. / To fit (pieces of a mechanical assembly) with a key to maintain the orientation between them. / To mark or indicate with a symbol indicating membership in a class.

Alternative form of quay.

One of a string of small islands.

(slang) Clipping of kilogram (especially of a recreational drug)

An object designed to open and close a lock. / An object designed to fit between two other objects (such as a shaft and a wheel) in a mechanism and maintain their relative orientation.

(transitive) To put (someone) into (a particular state, emotion etc.). / (intransitive) To cohere with; to accord with, to be in keeping with.

(transitive) to enter data by keyboarding

A surname.

(figuratively) In harmony, accord, or sympathy (with); congruent.