Start mining gold in a small way (5)
I believe the answer is:
minor
'a small way' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'start mining gold' is the wordplay.
'start mining' becomes 'min' (I can't explain this - if you can you should give a lot more credence to this answer).
'gold' becomes 'or' ('or' is the heraldic name for gold).
'min'+'or'='MINOR'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for minor that I've seen before include "Of less importance" , "Inconsequential" , "Under-age or of little importance" , "Slight; little known" , "Young person below voting age" .)