big-sisterly adjective 1adverb 1forms 2 adjective1 •Of or characteristic of older sisters.Some were sweet and big-sisterly, good shoulders to cry on; others eternal cheerleaders, all freckles and bobby sox; still others were serious campus leaders with their blond hair in a severe twist. — 1988 adverb1 •In the manner of an older sister.By turns she could be goofy and serious, playful and big-sisterly stern. — 2015 formsmore big-sisterly · most big-sisterly