Catalogue biological grouping if unknown (8)
I believe the answer is:
classify
'catalogue' is the definition.
(I know that catalogue is a kind of classify)
'biological grouping if unknown' is the wordplay.
'biological grouping' becomes 'class' (class is a kind of grouping. I am not sure about the 'biological' bit.).
'unknown' becomes 'y' (algebra).
'class'+'if'+'y'='CLASSIFY'
Can you help me to learn more?
(Other definitions for classify that I've seen before include "Arrange systematically by group (8)" , "Arrange by category" , "catalogue?" , "Arrange in divisions" , "Arrange in categories" .)