ズボン下した

noun

long underwear; long johns; thermal underpants

Refers to full-length underpants worn under trousers, often for warmth. Common in cold weather.

• 冬ふゆはズボン下したを履はくと暖あたたかい。

  In winter, wearing long underwear keeps you warm.

• スキーに行いく前まえにズボン下したを買かった。

  I bought long johns before going skiing.