Merriam-Webster's Collegiate® Dictionary, 11th Edition
RESPONDENT
I. noun
Etymology: Latin respondent-, respondens, present participle of respondēre
Date: 1528
one who responds: as, one who maintains a thesis in reply, b. one who answers in various legal proceedings (as in equity cases), the prevailing party in the lower court, a person who responds to a poll, a reflex that occurs in response to a specific external stimulus,
II. adjective
Date: 1726
making response ; responsive , relating to or being behavior or responses to a stimulus that are followed by a reward