Identified as a specific type; famous, renowned. / Accepted, familiar, researched.

Any fact or situation which is known or familiar. / (algebra) A constant or variable the value of which is already determined.

past participle of know

The fact of knowing about something; general understanding or familiarity with a subject, place, situation etc.

(obsolete) To confess as true; to acknowledge.

A utensil or a tool designed for cutting, consisting of a flat piece of hard material, usually steel or other metal (the blade), usually sharpened on one edge, attached to a handle. The blade may be pointed for piercing.

(transitive) To cut with a knife. / (transitive) To use a knife to injure or kill by stabbing, slashing, or otherwise using the sharp edge of the knife as a weapon.

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.

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.