Responsibility — and where ours lies (4)
I believe the answer is:
onus
'responsibility' is the definition.
(thesaurus)
'and where ours lies' is the wordplay.
I cannot quite understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
The remaining letters 'ous' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
(Other definitions for onus that I've seen before include "Capulet opponent (R&J)" , "Liability" , "Weight of responsibility" , "'Burden, load (4)'" , "Burden, duty" .)