Saw wanderer in empty pub (7)
I believe the answer is:
proverb
'saw' is the definition.
(a saw can mean a proverb or maxim)
'wanderer in empty pub' is the wordplay.
'wanderer' becomes 'rover' (synonyms).
'in' means one lot of letters goes inside another.
'empty' means to remove the middle letters.
'pub' with its centre taken out is 'pb'.
'rover' placed inside 'pb' is 'PROVERB'.
(Other definitions for proverb that I've seen before include "Wise saying" , "Old saying, perhaps by Solomon?" , "Well-known statement incorporating general truth" , "Old saw" , "Pithy saying expressing a general truth" .)