Chief less sensitive when eighty-three, say (5,6)
I believe the answer is:
prime number
'three say' is the definition.
(I know that 3 is a near-square prime)
'chief less sensitive' is the wordplay.
'chief' becomes 'prime' (I've seen this before).
'less sensitive' becomes 'number' (numb means insensitive or unfeeling).
'prime'+'number'='PRIME NUMBER'
'when eighty' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for prime number that I've seen before include "2 or 3 -- but not 4" , "one alone can always divide" , "One such as 3, 5, 7, 11, etc" , "Two or three perhaps" , "Integer divisible only by itself and by 1" .)