"simple, plain, not compound," 1844, from simple, adj. + -istic. From 1867 as "over-simple, trying to explain too much by a single principle." Also (1860) "of or pertaining to simples" (herbs used in healing, medicine of one ingredient only; the notion being that each herb possesses a particular virtue, thus a "simple" remedy), from simplist "one who studies simples" (1590s; see simple, adj.) + -ic.