Volunteer: a person who freely offers to take part in an enterprise or undertake a task. ( ~5 W+ m" y) E! L2 }* bsynonyms: subject, participant, case, patient; informalguinea pig - E/ i, [( R$ v( |' D7 r8 j"each volunteer was tested three times"/ [6 W3 {6 Z" b, P/ @3 k0 C' ?0 n