Not so sensitive an issue? (6)
I believe the answer is:
number
This clue is a double definition.
'not so sensitive' is the first definition.
(I've seen this before)
'an issue?' is the second definition.
('number' can be a synonym of 'issue')
(Other definitions for number that I've seen before include "Digit, cipher" , "For example, one" , "Is it sung" , "Quantity, amount; song" , "(Symbol for) quantity" .)