boughyoudaoicibaDictYouDict[bough 词源字典]
bough: [OE] Bough is a word of some antiquity, dispersed far and wide throughout the Indo- European languages, but it is only in English that it has come to mean ‘branch’. It comes ultimately from an Indo-European *bhāghūs; the meaning this had is not altogether clear, but many of its descendants, such as Greek pakhus and Sanskrit bāhús, centre semantically round ‘arm’ or ‘forearm’ (a meaning element which can be discerned in the possibly related bosom).

Germanic adopted the Indo-European form as *bōgus, with apparently a shift in signification up the arms towards the shoulders (Old English bōg, bōh, Old Norse bógr, and Middle Dutch boech all meant ‘shoulder’, and the Dutch word later came to be applied to the front of a ship – possibly the source of English bow).
=> bosom, bow[bough etymology, bough origin, 英语词源]
bough (n.)youdaoicibaDictYouDict
Old English bog "shoulder, arm," extended in Old English to "twig, branch" (compare limb (n.1)), from Proto-Germanic *bogaz (cognates: Old Norse bogr "shoulder," Old High German buog, German Bug "shoulder, hock, joint"), from PIE *bhagus "elbow, forearm" (cognates: Sanskrit bahus "arm," Armenian bazuk, Greek pakhys "forearm"). The "limb of a tree" sense is peculiar to English.