Saw wanderer is in lead (7)
I believe the answer is:
proverb
'saw' is the definition.
(a saw can mean a proverb or maxim)
'wanderer is in lead' is the wordplay.
'wanderer' becomes 'rover' (synonyms).
'is in' indicates putting letters inside.
'lead' becomes 'Pb' (Pb is the chemical symbol for lead).
'rover' going into 'pb' is 'PROVERB'.
(Other definitions for proverb that I've seen before include "Well-known statement incorporating general truth" , "Generally true saying" , "Saying of great truth" , "Aphorism" , "Pithy saying expressing a general truth" .)