Big fan that's in use irregularly (10)

I believe the answer is:

enthusiast

I'm a little stuck... Click here to teach me more about this clue!

'big fan' is the definition.
'enthusiast' can be an answer for 'fan' (I've seen this before). I'm unsure of the 'big' bit.

'that's in use irregularly' is the wordplay.
'irregularly' is an anagram indicator.
'thats'+'in'+'use'='thatsinuse'
'thatsinuse' is an anagram of 'ENTHUSIAST'.

Can you help me to learn more?

(Other definitions for enthusiast that I've seen before include "Ardent supporter" , "one not at all cool" , "Devotee" , "buff" , "One deeply interested in a subject" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.