Husband has more on new chemical (7)
I believe the answer is:
hormone
'chemical' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'husband has more on new' is the wordplay.
'husband' becomes 'h' (abbreviation).
'has' means one lot of letters go next to another.
'new' indicates an anagram.
'more'+'on'='moreon'
'moreon' with letters rearranged gives 'ormone'.
'h'+'ormone'='HORMONE'
Can you help me to learn more?
(Other definitions for hormone that I've seen before include "Secretion transported in the blood" , "chemical constituent" , "Internal secretion - moorhen (anag)" , "Compound" , "Stimuating substance produced by body" .)