Say, Gold can put back Nano component of atmosphere (8)
I believe the answer is:
nitrogen
'component of atmosphere' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'say gold can put back nano' is the wordplay.
'say' becomes 'eg'.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'can' becomes 'tin' (synonyms).
'put back' shows that the letters should be reversed in order.
'nano' becomes 'n' (this might be a standard abbreviation of which I'm unaware).
'eg'+'or'+'tin'='egortin'
'egortin' reversed gives 'nitroge'.
'nitroge'+'n'='NITROGEN'
Can you help me to learn more?
(Other definitions for nitrogen that I've seen before include "Gas forming 78% of the air" , "Gas forming about four-fifths of atmosphere" , "Neon grit (anag.)" , "Constituent of four fifths of earth's atmosphere" , "Main gas in air" .)