Английский Этимологический словарь - simple

- 12c., from O.Fr. simple, from L. simplus "single." Originally "humble, ignorant," sense evolved to "lowly, common" (c.1280), then "mere, pure" (1303). As opposite of composite it dates from 14c.; as opposite of complicated it dates from c.1555. Disparaging sense (M.E.) is from notion of "devoid of duplicity." Simply (adv.) in purely intensive sense is from 1590.