Comparatively insensitive song, say? (6)
I believe the answer is:
number
This clue might be a double definition.
'comparatively insensitive' is the first definition.
('numb' can be a synonym of 'insensitive')
'song say?' is the second definition.
The definition and answer can be both to do with communicating as well as being verbs in their base form.
Perhaps there's a link between them I don't understand?
Can you help me to learn more?
(Other definitions for number that I've seen before include "Comparatively torpid" , "Is it sung" , "Having less feeling - quantity" , "less sensitive" , "(Symbol for) quantity" .)