drafting instrument used to draw or measure angles
protractor详细解释
pro.trac.tor n.（名词）Mathematics A semicircular instrument for measuring and constructing angles.【数学】 量角器：一种半圆形的量角和画角的工具An adjustable pattern used by tailors.裁缝使用的可调整的图型Anatomy A muscle that extends a limb or other part.【解剖学】 伸肌：一块伸展肢体或其它部份的肌肉
