Maxim's dog in empty pub (7)
I believe the answer is:
proverb
'maxim's' is the definition.
(I've seen this before)
'dog in empty pub' is the wordplay.
'dog' becomes 'rover' (Rover is a common name for a pet dog).
'in' is an insertion indicator.
'empty' suggests removing the centre.
'pub' with its middle removed is 'pb'.
'rover' inserted into 'pb' is 'PROVERB'.
(Other definitions for proverb that I've seen before include "Old saying, perhaps by Solomon?" , "encapsulate wisdom" , "gnome" , "Adage, pithy saying" , "OT saying" .)