Ruin; annihilate (7)
I believe the answer is:
destroy
This clue is a double definition.
'ruin' is the first definition.
(synonyms)
'annihilate' is the second definition.
(I've seen this before)
(Other definitions for destroy that I've seen before include "put to death" , "Soundly defeat" , "'Demolish, ruin (7)'" , "Get rid of" , "Kill; ruin" .)