armpit

腋 is composed of the BuShou of 肉(meat) and 夜(night). 夜 can be seen as the compound of 亦(the picture of a man showing his armpits) and 月(the moon), the original meaning of 亦 is armpit, armpits are alway covered, which has the meaning of darkness and 月 is added in order to emphasize it, since 夜 is used to represent the meaning of night, so 肉 is added and make 腋 to mean armpit.