Kill one in ten (8)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
decimate
(Other definitions for decimate that I've seen before include "Aimed etc in order to destroy a large proportion of" , "Reduce by a tenth" , "Medicate (anag.)" , "By killing" , "Kill one in ten (as Romans did as punishment for mutiny)" .)