From Longman Dictionary of Contemporary Englishsisterlysis‧ter‧ly /ˈsɪstəli $ -ər-/ adjective FRIENDLYtypical of a loving sister → brotherly She gave Lee a sisterly kiss. Their friendship can best be described as sisterly.
Examples from the Corpus
sisterly• Let's talk about something more sisterly.• She leaned forward to give her departing visitor a kiss that could hardly have been described as sisterly.• The friendship between the Girls can aptly be described as sisterly.• Well, possibly more than sisterly.• sisterly affection• This can hardly be described as sisterly behaviour.• Serena is torn between her sisterly love and her annoyance with Stella's aggressive insecurity.• Her eyes blazed with her fierce sisterly love of him.• Then pulls me down beside her, and gives me a sisterly squeeze. 