c. 1300, in reference to vows or compacts, from un- (1) "not" + broken. Attested from late 15c. in reference to material things; 1510s in reference to courage, spirit, etc.; 1530s in reference to horses; 1560s in reference to the flow of time. Old English had ungebrocen.[unbroken etymology, unbroken origin, 英语词源]