He's not bored. Hello! It's a brothel! (8)
I believe the answer is:
bordello
'it's a brothel' is the definition.
(synonyms)
'he's not bored hello' is the wordplay.
'he' becomes 'Bord'.
'not bored hello' becomes 'ello' (I can't explain this - if you can you should give a lot more credence to this answer).
'bord'+'ello'='BORDELLO'
Can you help me to learn more?
(Other definitions for bordello that I've seen before include "Knocking shop" , "Madam's house" , "Congress here" , "12 across (anag)" , "Disorderly house" .)