enthusiast; zealot; fanatic
Refers to a person who is passionately devoted to a cause, hobby, or activity. Can range from positive enthusiasm to excessive fanaticism depending on context.
He is a passionate soccer fan, truly an enthusiast.
The politician's zealots devoted themselves entirely to the campaign.
Compound of 熱狂 (nekkyō, 'wild enthusiasm') + 者 (sha, 'person'). The reading ねっきょう reflects a common gemination (促音便) from ねつきょう.