Number ten is a cheat, somehow (11)
I believe the answer is:
anaesthetic
'number' is the definition.
(something which 'numbs' you)
'ten is a cheat somehow' is the wordplay.
'somehow' indicates an anagram.
'ten'+'is'+'a'+'cheat'='tenisacheat'
'tenisacheat' is an anagram of 'ANAESTHETIC'.
(Other definitions for anaesthetic that I've seen before include "A number of theatres" , "Theatre number" , "Drug that causes temporary loss of feeling" , "Number of bodies - can hesitate (anag)" , "Numbing substance" .)