Lead-free metal is on gold gnasher (7)
I believe the answer is:
incisor
'gnasher' is the definition.
I can't tell whether this definition defines the answer.
'lead-free metal is on gold' is the wordplay.
'lead-free' means to remove the first letter (the letter which leads the word is removed).
'metal' becomes 'zinc' (zinc is a kind of metal).
'on gold' becomes 'or' ('or' is the heraldic name for gold. I am not sure about the 'on' bit.).
'zinc' with its initial letter removed is 'inc'.
'inc'+'is'+'or'='INCISOR'
Can you help me to learn more?
(Other definitions for incisor that I've seen before include "Cutting tooth" , "Ivory perhaps" , "companion could be Goofy" , "Type of tooth" , "Canine" .)