Volunteer: a person who freely offers to take part in an enterprise or undertake a task. - i l$ z/ l0 Qsynonyms: subject, participant, case, patient; informalguinea pig 5 E \* O& I2 f' f5 V"each volunteer was tested three times" 3 W+ N+ ^9 r7 G- v( l' @5 Y# I+ h