Singular type of number (3)
I believe the answer is:
odd
'singular' is the definition.
(I know that singular can be written as odd)
'type of number' is the wordplay.
'type of' becomes 'od' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'number' becomes 'D' (D is an example).
'od'+'d'='ODD'
Can you help me to learn more?
(Other definitions for odd that I've seen before include "like half the numbers?" , "It's certainly not even" , "Left over" , "like twenty two [FIFTEEN]? Yes and no!" , "Peculiar or unpaired" .)