Maxim runs over in empty pub (7)
I believe the answer is:
proverb
'maxim' is the definition.
(I know that maxim can be written as proverb)
'runs over in empty pub' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'in' means one lot of letters goes inside another.
'empty' says to hollow out the word (remove centre letters).
'pub' with its middle removed is 'pb'.
'r'+'over'='rover'
'rover' put into 'pb' is 'PROVERB'.
(Other definitions for proverb that I've seen before include "Old saw" , "Maxim" , "Adage, pithy saying" , "Short saying expressing a supposed truth" , "Pithy saying expressing a general truth" .)