Class fool, otherwise term for clot (6)
I believe the answer is:
assort
'class' is the definition.
(I know that class can be written as assort)
'fool otherwise term for clot' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'otherwise' becomes 'or'.
'term for' suggests the final letters (the letter which terminates the word).
The final letter of 'clot' is 't'.
'ass'+'or'+'t'='ASSORT'
(Other definitions for assort that I've seen before include "Categorize" , "(Of genes) become distributed among cells" , "Categorise" , "Classify, arrange in groups" , "Class" .)