weak sister noun2 •(US) A person or thing which is the least robust or least dependable member of a group.San Antonio has always been viewed as the weak sister of the big regional centers of Houston and Dallas. — 1991 •(US, disapproving) A person who is cowardly or indecisive."Your course of action this past year has bordered on criminal negligence," he barks to the man whose job he means to take. "You're a weak sister, Mr. President." — 1964 formsweak sisters
