Dine regularly at first in the playhouse (7)
I believe the answer is:
theatre
'playhouse' is the definition.
(thesaurus)
'dine regularly at first in the' is the wordplay.
'dine' becomes 'eat' (I've seen this before).
'at first' indicates taking the first letters.
'in' means one lot of letters goes inside another.
The first letter of 'regularly' is 'r'.
'eat'+'r'='eatr'
'eatr' put within 'the' is 'THEATRE'.
(Other definitions for theatre that I've seen before include "Place for stage works" , "Audience" , "Building for plays or operations" , "Location for plays and operations" , "US cinema" .)