plighter

noun

1. One who or that which plights, engages, or pledges.

   “My playfellow, your hand; this kingly seal And plighter of high hearts!”

   “I mean to say, remorse has frequently been known to set in after a dust-up between a couple of troth-plighters, with all that Sorry-I-was-cross and Can-you-ever-forgive-me stuff, and love, after being down in the cellar for a time with no takers, perks up and carries on again as good as new.”

   “He hung up. And felt stupid. The most beautiful woman in the whole world had practically plighted her troth to him. And she didn’t seem like your run-of-the-mill plighter.”