"follower of fashion," by 1830, from mode (n.2) + -ist.
Entries linking to modist
mode n.2
"current fashion, prevailing style," 1640s, from French mode "manner, fashion, style" (15c.), a specialized use of the French word that also yielded mode (n.1).
-ist
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.