Old English sculdor "shoulder," from West Germanic *skuldro (source also of Middle Dutch scouder, Dutch schouder, Old Frisian skoldere, Middle Low German scholder, Old High German scultra, German Schulter), of unknown origin, perhaps related to shield (n.). Meaning "edge of the road" is attested from 1933. Cold shoulder (Nehemiah ix.29) translates Latin humerum recedentum dare in Vulgate (but see cold shoulder). Shoulder-length, of hair, is from 1951.
c. 1300, "to push with the shoulder," from shoulder (n.). Meaning "take a burden" first recorded 1580s. The military sense is from 1590s. Related: Shouldered; shouldering.