engager

noun

1. One who, or that which, engages.

   “engagers in conflicts”

2. One who, or that which, engages.

   “To address this limitation, strategies for redirecting T cells to treat cancer are being intensively investigated, while the bispecific T cell engager (BiTE) therapy constitutes one of the most promising therapeutic approaches.”

3. One who enters into an engagement or agreement; a surety.

   “Several sufficient citizens were engagers.”