expression, godan verb (-gu)
lend a hand; help out; pitch in
Idiomatic expression meaning to actively help someone, often by joining in physical work or making a real effort. Conveys a sense of rolling up one's sleeves and getting involved.
引っ越しのとき、友達が片肌脱いでくれた。
When I moved, my friend pitched in and helped.
彼は
Whenever he sees someone in trouble, he immediately lends a hand.
expression, godan verb (-gu)
bare one shoulder
Literal meaning of the phrase: to expose one shoulder by slipping off clothing. This literal sense is rarely used in modern conversation; the idiomatic sense is overwhelmingly more common.
祭りの準備で、男たちは片肌脱いで神輿を担いだ。
During the festival preparations, the men bared one shoulder and carried the portable shrine.