Thrash late attendee's bottom (5)
I believe the answer is:
paste
'thrash' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for paste that I've seen before include "Creamy, sticky, or doughy mixture" , "Adhesive of mixed water and flour" , "Fake gems; adhesive" , "Adhesive; savoury spread" , "sound beating" .)