Thrashes (5)
'thrashes' is the definition.
('beat' can be a synonym of 'thrash')
This is the entire clue.
(Other definitions for beats that I've seen before include "Buffets" , "Rhythms" , "Regular routes for policemen" , "Tans" .)
(Another definition for trounces that I've seen is " Defeats thoroughly".)
'thrashes' is the definition.
(I've seen this in another clue)
This is all the clue.
(Another definition for lams that I've seen is " Attacks".)