Big league auctioneer's covering empty garage (5)
I believe the answer is:
large
'big' is the definition.
(synonyms)
'league auctioneer's covering empty garage' is the wordplay.
'league' becomes 'l' (abbreviation).
'covering' suggests removing the centre (the letters which cover the word are used).
'empty' suggests removing the centre.
'auctioneer' with its middle taken out is 'ar'.
'garage' with its middle removed is 'ge'.
'l'+'ar'+'ge'='LARGE'
(Other definitions for large that I've seen before include "Immense" , "Big < burly" , "Strapping" , "Big, almost regal" , "Sizeable" .)