behalf: [14] Behalf was compounded from the prefix be- ‘by’ and the noun half, in the sense ‘side’. The latter had been used in such phrases as on my half, that is, ‘on my side, for my part’, since late Old English times, and the new compound began to replace it in the 14th century. (That particular use of half had died out by the end of the 16th century.) The modern sense of ‘representing or in the interests of someone’ was present from the beginning. => half[behalf etymology, behalf origin, 英语词源]