Volunteer: a person who freely offers to take part in an enterprise or undertake a task. 3 Y' w+ K, B8 K+ b* Bsynonyms: subject, participant, case, patient; informalguinea pig. r9 M& v# U$ `0 J+ X) g
"each volunteer was tested three times" 8 F5 _- g3 [% w9 \. \& b( s) T' D+ a