Note: Pointer’s thin (6)
I believe the answer is:
narrow
'thin' is the definition.
(associated in meaning)
'note pointer's' is the wordplay.
'note' becomes 'n' (abbreviation).
'pointer' becomes 'arrow' (synonyms).
'n'+'arrow'='NARROW'
(Other definitions for narrow that I've seen before include "limit" , "Close shave" , "Fine" , "Vessel designed for canals" , "Strait, not broad" .)