Thoughtless, inattentive (8)
I believe the answer is:
careless
I believe this is a double definition.
'thoughtless' is the first definition.
(similar in meaning)
'inattentive' is the second definition.
(associated in meaning)
(Other definitions for careless that I've seen before include "Negligent, unconcerned" , "Inattentive to one's work" , "Unthinking and irresponsible" , "Not paying enough attention" , "Cavalier" .)