Volunteer: a person who freely offers to take part in an enterprise or undertake a task. ; X( ^% K- E o1 \synonyms: subject, participant, case, patient; informalguinea pig) r& W. z, U: N9 U3 b, m
"each volunteer was tested three times" 5 k6 Q# T+ n& y) ~1 I$ L0 \1 V0 T