Hostile Finn rudely waving (10)
I believe the answer is:
unfriendly
'hostile' is the definition.
(I know that hostile can be written as unfriendly)
'finn rudely waving' is the wordplay.
'waving' indicates an anagram (letters wave around).
'finn'+'rudely'='finnrudely'
'finnrudely' with letters rearranged gives 'UNFRIENDLY'.
(Other definitions for unfriendly that I've seen before include "Disagreeable" , "Aggressive" , "Hostile" .)