1. Unselfishly concerned for or devoted to the welfare of others.
And, a bit of a surprise:
2.Animal Behavior. Of or pertaining to behavior by an animal that may be to its disadvantage but that benefits others of its kind, often its close relatives.
With etymological references:
I thought you were an altruistic banker, nothing more, nothing less. A civic-mindedaltruistic banker.
— Inman Majors, The Millionaires: A Novel
An altruistic act is an act performed for the welfare of others. It is unselfish, as opposed to an act performed for self, which is selfish.
— Jack London, The Sea-Wolf
Altruistic was coined in 1830 by philosopher Auguste Comte. It originates in the French word altruimeaning “of or to others” from the Latin word alteri meaning “other.”