subtle

The adjective is derived from Middle English sotil, soubtil, subtil (“of a person, the mind, etc.: clever, ingenious, penetrating; cunning, sly; insidious; delicate, fine; not dense, light, thin; finely powdered; narrow, slender; etc.”), borrowed from Anglo-Norman sotel, subtil, sutil, Middle French soutil, subtil, sutil, and Old French sotil, soutil, subtil, sutil (“of an object: skilfully designed or made; delicate, fine; slender, thin; of an intangible thing: difficult to understand; of a person: discerning, shrewd; devious, sly; etc.”) (modern French subtil), from Latin subtīlis (“of texture: delicate, fine; slender, thin; accurate, keen; having fine judgment; etc.”), from sub (“below, under”) + tēla (“warp (threads running lengthwise in a loom); web”) (ultimately from Proto-Indo-European tetḱ- (“to create, produce; to cut, hew”), from teḱ- (“to beget, sire”)). The word displaced Old English smēag (literally “creeping”). The modern and Middle English (and French) spellings with -b- are influenced by Latin subtīlis; the letter was probably never pronounced. The noun is derived from Middle English sotil, soubtil, subtil (“wise person; sophisticated people collectively”), from the adjective.

Partly from both of the following: * From Middle English sotilen, subtile, subtilien (“to reflect on (something); to become mentally keen; to connive, scheme; to contrive, invent; to become pure or thin; to (cause something to) become light or thin; (medicine) to lighten or reduce (a diet)”), from Anglo-Norman sotiller, soutiller, sutiller, Middle French soutiller, soutillier, and Old French soutillier (“to make thin; to sharpen; to split hairs when arguing; to scheme, plot”), from Old French sotil, soutil, subtil, sutil (noun) (see etymology 1) + -ier (suffix forming infinitives of first-conjugation verbs), partly influenced by Late Latin subtīliāre, the present active infinitive of subtīliō (“to act craftily; to diminish”), from Latin subtīlis (adjective) (see etymology 1) + -ō (suffix forming regular first-conjugation verbs). * From subtle (adjective).