Well-known oaf must, in short, be thrown out (6)
I believe the answer is:
famous
'well-known' is the definition.
(I've seen this in another clue)
'oaf must in short be thrown out' is the wordplay.
'in short' means to remove the last letter.
'be thrown out' is an anagram indicator.
'oaf'+'must'='oafmust'
'oafmust' with its last letter taken away is 'oafmus'.
'oafmus' with letters rearranged gives 'FAMOUS'.
(Other definitions for famous that I've seen before include "Well-known" , "Eminent" , "Known-of widely" , "Acclaimed" , "Widely-known" .)