Nine let out: that's compassionate (7)
I believe the answer is:
lenient
'that's compassionate' is the definition.
(I've seen this before)
'nine let out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'nine'+'let'='ninelet'
'ninelet' is an anagram of 'LENIENT'.
(Other definitions for lenient that I've seen before include "Soft on the rules" , "Mild and tolerant" , "Soft-hearted" , "Inclined to let people off lightly" , "Tolerant, rather than strict" .)