1530s, "of or pertaining to Greek philosopher Plato" (429 B.C.E.-c. 347 B.C.E.), from Latin Platonicus, from Greek Platōnikos. The name is Greek Platōn, a nickname in reference to his broad shoulders (from platys "broad;" from PIE root *plat- "to spread"); his original name was Aristocles, son of Ariston. The meaning "free of sensual desire" (1630s, in Platonic love "pure spiritual affection unmixed with sexual desire," translating Latin Amor platonicus) which the word usually carries nowadays, is a Renaissance notion; it is based on Plato's writings in "Symposium" about the kind of interest Socrates took in young men and originally had no reference to women. Related: Platonically.
The bond which unites the human to the divine is Love. And Love is the longing of the Soul for Beauty ; the inextinguishable desire which like feels for like, which the divinity within us feels for the divinity revealed to us in Beauty. This is the celebrated Platonic Love, which, from having originally meant a communion of two souls, and that in a rigidly dialectical sense, has been degraded to the expression of maudlin sentiment between the sexes. Platonic love meant ideal sympathy ; it now means the love of a sentimental young gentleman for a woman he cannot or will not marry. [George Henry Lewes, "The History of Philosophy," 1867]
word-forming element meaning "one who does or makes," also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista (source also of Spanish, Portuguese, Italian -ista), from Greek agent-noun ending -istes, which is from -is-, ending of the stem of verbs in -izein, + agential suffix -tes.
Variant -ister (as in chorister, barrister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish, popularized in American English 1970s by names of Latin-American revolutionary movements.