noun
one elbow
Refers to a single elbow, often used in contexts where one elbow is propped on a surface or contrasted with both elbows.
彼は片肘を机について考え込んだ。
He rested one elbow on the desk and was lost in thought.
肘 is the general word for elbow(s); 片肘 specifically means one elbow.
Compound of 片 (kata, 'one side') and 肘 (hiji, 'elbow').