Careless line failing to impress good man (9)
I believe the answer is:
negligent
'careless' is the definition.
(associated in meaning)
'line failing to impress good man' is the wordplay.
'failing' indicates an anagram (a failed spelling of the word).
'to impress' means one lot of letters goes inside another (impress can mean enlist or recruit).
'good' becomes 'g' (abbreviation).
'man' becomes 'gent' (gent is a kind of man).
'line' anagrammed gives 'neli'.
'neli' placed around 'g' is 'negli'.
'negli'+'gent'='NEGLIGENT'
(Other definitions for negligent that I've seen before include "Of the study of insects" , "Lax" , "Not taking due care" , "slack" , "Failing to take proper care" .)