Category, grouping (5)
I believe the answer is:
class
This clue is a double definition.
'category' is the first definition.
(I know that category can be written as class)
'grouping' is the second definition.
(I know that class is a type of taxon)
(Other definitions for class that I've seen before include "Lesson; social division" , "Excellent" , "Genre" , "Body of students" , "pupils?" .)