How unfeeling it is, to call us out for nothing (7)
I believe the answer is:
callous
'how unfeeling' is the definition.
'callous' can be an answer for 'unfeeling' (synonyms). I'm unsure of the 'how' bit.
'it is to call us out for nothing' is the wordplay.
'it' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'is to' means one lot of letters go next to another (I've seen this in other clues).
'out' means to remove the last letter.
'for' means one lot of letters go next to another (I've seen this in other clues).
'nothing' becomes 'O' (O resembles 0).
'us' with its final letter removed is 'u'.
'u' after 'o' is 'ou'.
'call'+'ou'='callou'
's' after 'callou' is 'CALLOUS'.
Can you help me to learn more?
(Other definitions for callous that I've seen before include "Cruel or unsympathetic" , "Hard-hearted" , "Not feeling" , "Heartless" , "Cruelly unfeeling" .)