One Who Chooses Not to Participate in a Proposal

Puzzle 15 of Classic Things Medium Pack

Question is: One Who Chooses Not to Participate in a Proposal

and the answer is: ABSTAINER

Word Meaning:

ABSTAINER — One who abstains; especially, one who abstains from something, such as the use of alcohol or drugs, or one who abstains for religious reasons; one who practices self-denial.

Definitions from Wiktionary.