Ambassador has honour, and he admits not being a tenant (9)
I believe the answer is:
homeowner
'ambassador has honour and he admits not being a tenant' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'ambassador has honour and he' is the wordplay.
'ambassador' becomes 'he' (His or Her Excellency).
'has' means one lot of letters goes inside another.
'honour' becomes 'om'.
'and' says to put letters next to each other.
'he' becomes 'owner' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'he' going around 'om' is 'home'.
'home'+'owner'='HOMEOWNER'
Can you help me to learn more?
(Other definitions for homeowner that I've seen before include "One with their own property" , "landlord?" .)