Saw wanderer entering empty pub (7)
I believe the answer is:
proverb
'saw' is the definition.
(a saw can mean a proverb or maxim)
'wanderer entering empty pub' is the wordplay.
'wanderer' becomes 'rover' (synonyms).
'entering' is an insertion indicator.
'empty' means to remove the middle letters.
'pub' with its centre removed is 'pb'.
'rover' put inside 'pb' is 'PROVERB'.
(Other definitions for proverb that I've seen before include "Maxim" , "Wise saying" , "Old saw" , "Generally true saying" , "Traditional saying" .)