Source : Webster's Revised Unabridged Dictionary (1913)

Sisterly \Sis"ter*ly\, a.
   Like a sister; becoming a sister, affectionate; as, sisterly
   kindness; sisterly remorse. --Shak.

Source : WordNet®

sisterly
     adj : like or characteristic of or befitting a sister; "sisterly
           kindness"; "sororal concern" [syn: {sisterlike}, {sororal}]
           [ant: {brotherly}]