Form; category (5)
I believe the answer is:
class
I believe this clue is a double definition.
'form' is the first definition.
(I know that form can be written as class)
'category' is the second definition.
(I know that category can be written as class)
(Other definitions for class that I've seen before include "Form; stylishness" , "Type; social level" , "Elegance - form" , "Fine" , "Order - quality" .)