1. [v]  choose or elect as a fellow member or colleague; "The church members co-opted individuals from similar backgrounds to replenish the congregation"
2. [v]  take or assume for one's own use; "He co-opted the criticism and embraced it"
3. [v]  appoint summarily or commandeer
4. [v]  neutralize or win over through assimilation into an established group; "We co-opted the independent minority tribes by pulling them into the Northern Alliance"

CO-OPT is a 6 letter word that starts with C.