A large number accustomed to being entertained (6)
I believe the answer is:
amused
'being entertained' is the definition.
('amused' can be a synonym of 'entertained')
'a large number accustomed' is the wordplay.
'large number' becomes 'm'.
'accustomed' becomes 'used' (I've seen this before).
'a'+'m'+'used'='AMUSED'
'to' is the link.
(Other definitions for amused that I've seen before include "Queen Victoria wasn't!" , "Delighted" , "Mildly entertained by Medusa" , "Tickled pink" , "Pleasantly occupied" .)