"elegant literature, literature as fine art," 1710, French, literally "fine letters," from belles, plural of belle, fem. of beau "fine, beautiful" (see beau) + lettres, plural of lettre "letter" (see letter (n.)). The literary equivalent of beaux arts; its boundaries never have been exact, and it is "now generally applied (when used at all) to the lighter branches of literature, or the æsthetics of literary study" [OED].
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.
<a href="https://www.etymonline.com/word/belletrist">Etymology of belletrist by etymonline</a>
Harper, D. (n.d.). Etymology of belletrist. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/belletrist