late 14c., "spoken, oral," from Old French vocal (13c.), from Latin vocalis "sounding, sonorous, speaking," as a noun, "a vowel," from vox (genitive vocis) "voice" (from PIE root *wekw- "to speak"). In reference to music (as opposed to instrumental), first recorded 1580s; meaning "outspoken" first attested 1871. Vocal cords is from 1872; see cord.
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/vocalist">Etymology of vocalist by etymonline</a>
Harper, D. (n.d.). Etymology of vocalist. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/vocalist