altruist

Concise Oxford English Dictionary © 2008 Oxford University Press:
altruism /ˈaltrʊɪz(ə)m/

▶noun selfless concern for the well-being of others.

■ Zoology behaviour of an animal that benefits another at its own expense.

– derivatives
altruist noun,
altruistic adjective,
altruistically adverb.

– origin C19: from Fr. altruisme, from Ital. altrui ‘somebody else’, from L. alteri huic ‘to this other’.