foil

\ \ English has three separate words foil. The oldest, ‘thwart’ [13], originally meant ‘trample’.

\ \ It probably comes via Anglo-Norman *fuler from Vulgar Latin *fullāre, a derivative of Latin fullō ‘person who cleans and bulks out cloth, originally by treading’ (whence English fuller [OE]). Foil ‘metallic paper’ [14] comes via Old French from Latin folium ‘leaf’ (source also of English foliage [15] and folio [16]). It originally meant ‘leaf’ in English too, but that usage died out in the 15th century. The modern notion of ‘one that enhances another by contrast’ comes from the practice of backing a gem with metal foil to increase its brilliancy, (Latin folium, incidentally, goes back to an Indo-European *bhel-, an extended form of which, *bhlō-, produced English blade, bloom, blossom, and flower.) The source of foil ‘sword’ [16] is not known, although the semantic development of blade from ‘leaf’ to ‘cutting part’ suggests the possibility that a similar process took place in the case of foil ‘leaf’.

\ \ Cf.⇒ FULLER; BLADE, BLOOM, BLOSSOM, FLOWER, FOLIAGE