Perhaps one could be less sensitive (6)
I believe the answer is:
number
This clue is a triple definition!
'perhaps one' is the first definition.
(one is a number)
'could' acts as a link.
'be' is the second definition.
(numbering is a kind of being)
'less sensitive' is the third definition.
(numb means insensitive or unfeeling)
(Other definitions for number that I've seen before include "42, say" , "Count, musical item" , "rational, possibly" , "One may be irrational or negative" , "For example, one" .)