内裤在英语中称为"underwear"，来源于英语单词"under"和"wear"的结合，"under"表示在下方，"wear"表示穿着。因此，"underwear"指的是穿在衣服下方的衣物。

例句：

I always wash my underwear after wearing it once. (我总是穿一次后就把我的内裤洗一次。)

Do you have any clean underwear in your suitcase? (你的手提箱里有没有干净的内裤？)

I need to buy some new underwear because mine are getting old and worn out. (我需要买一些新的内裤，因为我的内裤已经旧了并且穿坏了。)