engager

This term describes a person or entity that initiates a commitment, a social interaction, or a mechanical connection. In a professional or social context, it carries a connotation of proactivity and leadership, identifying the party that takes the first step to establish a relationship or agreement.

In mechanical engineering, the term refers specifically to a component that locks into another to transmit power. This technical usage is distinct from the social usage, as it describes a physical state of interlocking rather than a behavioral trait of initiation.