Volunteer: a person who freely offers to take part in an enterprise or undertake a task. ' @# T# b- W- D& H/ y1 k: P5 isynonyms: subject, participant, case, patient; informalguinea pig) P- U4 ?% `& m* R
"each volunteer was tested three times" , t6 y! {# r0 O4 L. l* U: [2 m