Not a Mr mistaken for a Mrs (6)
I believe the answer is:
matron
'a mrs' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'not a mr mistaken' is the wordplay.
'mistaken' is an anagram indicator.
'not'+'a'+'mr'='notamr'
'notamr' is an anagram of 'MATRON'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for matron that I've seen before include "Nurses' manager" , "Senior nurse" , "school officer" , "Chief nurse" , "Old woman" .)