The Collaborative International Dictionary of English v.0.48:
Sisterly \Sis"ter*ly\, a. Like a sister; becoming a sister, affectionate; as, sisterly kindness; sisterly remorse. --Shak. [1913 Webster]WordNet (r) 3.0 (2006):
sisterly adj 1: like or characteristic of or befitting a sister; "sisterly kindness"; "sororal concern" [syn: sisterly, sisterlike, sororal] [ant: brotherlike, brotherly, fraternal]