Feature of numbers with natural base (4)
I believe the answer is:
nose
'feature' is the definition.
(a facial feature)
'numbers with natural base' is the wordplay.
'numbers' becomes 'nos' ('no' is an abbreviation for number).
'with' is a charade indicator (letters next to each other).
'natural base' becomes 'e' (mathematical symbol. I am not sure about the 'natural' bit.).
'nos'+'e'='NOSE'
'of' is the link.
Can you help me to learn more?
(Other definitions for nose that I've seen before include "Cyrano's large feature" , "See 7" , "Organ of face" , "Bouquet of wine; beak" , "Front of an aircraft" .)