Beastly rival acquiring hotel at last (4)
I believe the answer is:
vile
'beastly' is the definition.
(synonyms)
'rival acquiring hotel at last' is the wordplay.
'rival' becomes 'vie' (I've seen this in other clues).
'acquiring' indicates putting letters inside.
'at last' says to take the final letters.
The final letter of 'hotel' is 'l'.
'vie' going around 'l' is 'VILE'.
(Other definitions for vile that I've seen before include "Horrible" , "Disgusting, quite evil" , "Book by Evelyn Waugh" , "Base" , "Very nasty, quite evil" .)