Altruistic (9)
(Other definitions for unselfish that I've seen before include "He's sinful, being altruistic" , "Considerate of the needs of others, altruistic" , "showing concern for others" , "Altruistic, not concerned with own interests" , "concerned for others?" .)
'altruistic' is the definition.
(synonyms)
This is all the clue.
(Other definitions for selfless that I've seen before include "Altruistic" , "Generous" , "Considerate" .)