1816, "underhand" (in reference to a style of throwing), from under + arm (n.1). First attested 1908 in dressmaking sense of "seams on the lower half of the arm-hole;" as a euphemism for armpit, it is attested from 1930s, popularized by advertisers.
权威例句
1. Practise throwing a ball underarm.
练习低手投球。
2. He got a sun - tanned underarm shoved up where the sun never shines!
他撸起日光曝晒的手臂上太阳永远照不到的地方!
3. To cut or slice ( a ball ) with an underarm stroke, as in tennis.
削球, 切球在网球中用下旋手法击 ( 球 )
4. But Hendrawan is excellent at playing overhead stokes and underarm strokes.
叶诚万的头顶击球和臂下击球都是绝好的.
5. Sniffed alone, the underarm odours smelled equally strong to men and women.