Upstart smells? About to produce decomposed organic mass? (5)
I believe the answer is:
humus
'produce decomposed organic mass?' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'upstart smells? about' is the wordplay.
'upstart' becomes 'u' (start of the word 'up').
'smells?' becomes 'hums' (I am not sure about this - if you are sure you should believe this answer much more).
'about' indicates putting letters inside.
'u' put within 'hums' is 'HUMUS'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for humus that I've seen before include "Organic "fertiliser"" , "Compost" , "decomposing organic matter" , "Decaying organic material" , "garden material" .)