Saw dog commonly held by lead (7)
I believe the answer is:
proverb
'saw' is the definition.
(synonyms)
'dog commonly held by lead' is the wordplay.
'dog commonly' becomes 'rover' (I've seen this before. I am not sure about the 'commonly' bit.).
'held by' means one lot of letters goes inside another.
'lead' becomes 'Pb' (Pb is the chemical symbol for lead).
'rover' put within 'pb' is 'PROVERB'.
Can you help me to learn more?
(Other definitions for proverb that I've seen before include "Adage, pithy saying" , "Aphorism" , "Maxim" , "encapsulate wisdom" , "Traditional saying" .)