Points to unknown biological characteristic (3)
I believe the answer is:
sex
'biological characteristic' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'points to unknown' is the wordplay.
'points' becomes 'se'.
'to unknown' becomes 'x' (algebra).
'se'+'x'='SEX'
Can you help me to learn more?
(Other definitions for sex that I've seen before include "VI (Lat.); m. or f." , "Gender" , "Expert in the treatment of coital problems" , "Hanky-panky" , "Male or female" .)