Division has key-men placed outside (7)
I believe the answer is:
segment
'division' is the definition.
(thesaurus)
'has key-men placed outside' is the wordplay.
'has key' becomes 'g' (I can't justify this - if you can you should give a lot more credence to this answer).
'placed' becomes 'set' ('set' can be a synonym of 'placed').
'outside' indicates putting letters inside.
'g'+'men'='gmen'
'gmen' going into 'set' is 'SEGMENT'.
Can you help me to learn more?
(Other definitions for segment that I've seen before include "One of several parts of a whole" , "Part separable from other parts, say of orange" , "Section of a circle" , "Piece of an orange" , "Separate" .)