breeches part

Hailed as "superfine" by a contemporary theatergoer, and not above playing the daring "breeches part" of a young man on stage, Nancy and her charms lured Washington to the theater five times in one week.

On the stage the phrase a “breeches” part is used when a woman plays in male costume.

I'm going to adopt the knee breeches part of it for good when I go home—golf breeches in the day time and knee breeches at night.