Always thoughtless? Doesn't matter (5,4)
I believe the answer is:
never mind
'doesn't matter' is the definition.
('never mind' means something doesn't matter)
'always thoughtless?' is the wordplay.
I cannot quite see how this works, but
'always' could be 'ever' (synonyms) and 'ever' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for never mind that I've seen before include "who cares?" , "It doesn't matter" , "Forget" , "Don't worry" .)