adoring, ardent, avid, big, dedicated, devoted, great, huge, keen (esp. BrE), loyal, number-one, real, true
I'm a big fan of Italian food.
one of the team's biggest fans
The singer says her dad is her number one fan.

lifelong, long-time
diehard, hard-core
Only diehard Tolkien fans will enjoy this book.

obsessive, rabid (humorous, esp. AmE)
a film that millions of rabid fans have waited years to see
The actress is asking the court to protect her from an obsessive fan.

casual (esp. AmE)
armchair (BrE)
For armchair fans back home, it was one of the highlights of the Olympics.

baseball, basketball, cricket, football, racing, rugby, soccer, sports, etc.
jazz, music, rock, etc.
film (esp. BrE), movie (esp. AmE)
home (esp. BrE)
The goal was greeted by jubilation from the home fans.

away (BrE), travelling (BrE), visiting (esp. BrE)
opposing, opposition (BrE), rival (esp. BrE)
There were clashes between opposing fans after the game.

be, become
I'm a big fan of her music.

delight, please, satisfy
The big band sound of Syd Lawrence and his Orchestra will delight fans.

attract
alienate
disappoint, let down
Fans will not be disappointed.

flock, gather, turn out, turn up
Tennis fans flocked to Wimbledon.
More than 40 000 fans turned up for the 12-hour event.

pack sth, pack into sth
Over 120 000 fans packed into the stadium.

line up (esp. AmE), queue (BrE), queue up (BrE), wait
watch sth
applaud (sb/sth), boo (sb/sth), chant sth, cheer (sb/sth)
Over 25 000 fans applauded both teams off the field.

clamour/clamor (for sth)
Hundreds of fans clamoured/clamored to catch a glimpse of the star.

club, site, website
letter, mail
fiction
I have a piece of fan fiction on their website.

base
The show has an extensive and loyal fan base.

electric
cooling
extractor
ceiling, overhead

blow
a fan blowing cold air

belt, blade, heater (esp. BrE)