He and I each represent one (7)
I believe the answer is:
element
'he' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Maybe there's an association between them I don't understand?
'and i each represent one' is the wordplay.
I cannot quite understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
'i' could be 'me' and 'me' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for element that I've seen before include "Constituent of universe" , "Wire in electric fire" , "Chemical building block" , "Constituent -- habitat" , "Basic substance or feature" .)