fractionyoudaoicibaDictYouDict[fraction 词源字典]
fraction: [14] Like fracture [15], which preserves its etymological meaning more closely, fraction comes ultimately from fractus, the past participle of Latin frangere ‘break’. This verb goes back to prehistoric Indo-European *bhr(e)g-, which also produced English break. The Latin derived noun fractiō simply meant ‘breaking’, particularly with reference to the breaking of Communion bread, but all trace of this literal sense has now virtually died out in English, leaving only the mathematical sense ‘number produced by division’ and its metaphorical offshoots.

Amongst the English meanings that have disappeared is ‘discord, quarrelling’, but before it went it produced fractious [18].
=> fracture, fragile, frail[fraction etymology, fraction origin, 英语词源]
fraction (n.)youdaoicibaDictYouDict
late 14c., originally in the mathematical sense, from Anglo-French fraccioun (Old French fraccion, "a breaking," 12c., Modern French fraction) and directly from Late Latin fractionem (nominative fractio) "a breaking," especially into pieces, in Medieval Latin "a fragment, portion," noun of action from past participle stem of Latin frangere "to break (something) in pieces, shatter, fracture," from Proto-Italic *frang-, from a nasalized variant of PIE root *bhreg- "to break" (cognates: Sanskrit (giri)-bhraj "breaking-forth (out of the mountains);" Gothic brikan, Old English brecan "to break;" Lithuanian brasketi "crash, crack;" Old Irish braigim "break wind"). Meaning "a breaking or dividing" in English is from early 15c.; sense of "broken off piece, fragment," is from c. 1600.