In our array, there's nothing even or odd for Napier (4)
I believe the answer is:
orra
'in our array there's nothing even' is the definition.
I know nothing about this answer so I can't tell whether this works.
'or odd for napier' is the wordplay.
'odd for napier' becomes 'ra' (I can't explain this - if you can you should give a lot more credence to this answer).
'or'+'ra'='ORRA'
Can you help me to learn more?
(Other definitions for orra that I've seen before include "Scotch left over" , "unmatched in Scotland" , "Occasional Scotch" .)