Flatten large beast, then sleep (8)
I believe the answer is:
bulldoze
'flatten' is the definition.
(I've seen this before)
'large beast then sleep' is the wordplay.
'large beast' becomes 'bull' (male cow).
'then' says to put letters next to each other.
'sleep' becomes 'doze' (doze means to sleep).
'bull'+'doze'='BULLDOZE'
(Other definitions for bulldoze that I've seen before include "Knock flat" , "get level" , "Clear with powerful tractor, demolish" , "Mechanically flatten" , "Railroad" .)