Словарь синонимов английского языка - voluntarily

(adv) freely, willingly, spontaneously, of (one's) own free will, on (one's) own (initiative or recognizance or responsibility), without prompting, without being prompded or asked, gratis, gratuitously; by choice, intentionally, purposely, on purpose, deliberately: Some of the ctudents spent their summer vacation voluntarily helping the needy.