sisterly /ˈsɪstəli/adjective 1adverb 1forms 4 adjective1 •Of or characteristic of sisters.Poor Mary [Austin] will do her very best and sisterliest for you. A kinder soul is not in the Earth. — 1864 adverb1 •In the manner of a sister, behaving as one would expect of a sister; as a sister, as sisters."What honest man, who is not insane, would take lost women and thieves into his house to dwell with him sisterly and brotherly?" — 1908 formsmore sisterly · sisterlier · most sisterly · sisterliest