the.com/devotee

means A devotee is someone who has given themselves over, intensely and often reverently, to a person, cause, belief, or pastime — more than enthusiasm, closer to allegiance.

from From Latin devovere, 'to vow away, consecrate' — the same root that gives us 'devote' and 'devotion.' It originally carried real religious weight: a devotee was someone who had vowed themselves to a deity or a sacred practice, body and will included. English borrowed the word in that spiritual sense before it loosened up to cover anyone pledged heart-and-soul to anything — opera, chess, a sports team — but the old vow-taking seriousness still clings to it.