Volunteer: a person who freely offers to take part in an enterprise or undertake a task." Q( }; y4 c0 E% O/ I& h% J$ m1 T& i& k' T
synonyms: subject, participant, case, patient; informalguinea pig; k G# ?3 u9 z% e# z: Z" i
"each volunteer was tested three times"8 O1 N2 K/ c% t6 v