Responsibility ours? (4)
I believe the answer is:
onus
'responsibility' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for onus that I've seen before include "Liability" , "Burden, duty" , "'Burden, load (4)'" , "'Burden, of proof (4)'" , "Obligation - charge" .)