PIE *skel, cut, cleaveから来た可能性があり、語源的にはscale, clone, cleaveと同じ。
英語の語源
half
half: [OE] Half comes from prehistoric Germanic *khalbaz, which also produced German halb, Dutch half, and Swedish and Danish halv. If, as some have suggested, it is connected with Latin scalpere ‘cut’ (source of English scalpel and sculpture) and Greek skóloph ‘spike’, its underlying meaning would be ‘cut, divided’.
half
Old English half, halb (Mercian), healf (W. Saxon) "side, part," not necessarily of equal division (original sense preserved in behalf), from Proto-Germanic *halbaz "something divided" (cognates: Old Saxon halba, Old Norse halfr, Old Frisian, Middle Dutch half, German halb, Gothic halbs "half"), perhaps from PIE (s)kel- (1) "to cut" (see shell (n.)). Noun, adjective, and adverb all were in Old English.
Used also in Old English phrases, as in modern German, to mean "one half unit less than," for example tridda healf "two and a half," literally "half third." The construction in two and a half, etc., is first recorded c. 1200. Of time, in half past ten, etc., first attested 1750; in Scottish, the half often is prefixed to the following hour (as in German, halb elf = "ten thirty"). To go off half-cocked in the figurative sense "speak or act too hastily" (1833) is in allusion to firearms going off prematurely; half-cocked in a literal sense "with the cock lifted to the first catch, at which position the trigger does not act" is recorded by 1750. In 1770 it was noted as a synonym for "drunk."
例文
1. Elliott crossed the finish line just half a second behind his adversary.エリオットはゴールラインを越えた時、相手より半秒遅れただけだった。
2.She 'd half expected him to withdraw from the course.
彼女は彼が途中で退出することを多少予想していた。
3.The French，who led 21-3 at half time，scored eight tries.
前半21：3でリードしたフランスは8得点だった。
4.The curtains were half drawn to cut out the sunlight.
カーテンを半分閉めて日光を遮った。
5.From what I hear， half the campus is lusting after her.