That legion slaughtered, number totally exposed (2,3,10)
I believe the answer is:
in the altogether
'exposed' is the definition.
(both can mean naked)
'that legion slaughtered number totally' is the wordplay.
'slaughtered' indicates anagramming the letters.
'number totally' becomes 'ether' (anaesthetic, something which numbs. I am not sure about the 'totally' bit.).
'that'+'legion'='thatlegion'
'thatlegion' with letters rearranged gives 'inthealtog'.
'inthealtog'+'ether'='IN THE ALTOGETHER'
Can you help me to learn more?
(Other definitions for in the altogether that I've seen before include "Naked" , "having nothing to wear?" , "exposed" , "wearing nothing?" , "barely seen" .)