Saw rambler in empty pub (7)
I believe the answer is:
proverb
'saw' is the definition.
('proverb' can be a synonym of 'saw')
'rambler in empty pub' is the wordplay.
'rambler' becomes 'rover' (I've seen this before).
'in' indicates putting letters inside.
'empty' says to hollow out the word (remove centre letters).
'pub' with its centre removed is 'pb'.
'rover' put into 'pb' is 'PROVERB'.
(Other definitions for proverb that I've seen before include "Make haste slowly, perhaps" , "Wise saying" , "Short saying expressing a supposed truth" , "'Adage, saw (7)'" , "Old saw" .)