Our first cardinal (3)
I believe the answer is:
one
'cardinal' is the definition.
(a cardinal number)
'our first' is the wordplay.
I cannot quite understand how this works, but
'our first' could be 'o' (1st letter of 'our') and 'o' is found within the answer.
The remaining letters 'ne' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for one that I've seen before include "joke" , "doesn't count for much" , "Unity" , "Half of two" , "Single and undivided" .)