an arm of a shirt 衬衫的袖子 He rolled up his shirtsleeves. 他卷起衬衣袖子。
Idioms
in (your) shirtsleeves
wearing a shirt without a jacket, etc. on top of it 只穿衬衫（未穿外衣） It was a hot day and most of the men were in shirtsleeves. 这一天天很热，大多数男子只穿着衬衫。