Squad also included in arrangement (7)
I believe the answer is:
platoon
'squad' is the definition.
(thesaurus)
'also included in arrangement' is the wordplay.
'also' becomes 'too' ('too' can be a synonym of 'also').
'included in' means one lot of letters goes inside another.
'arrangement' becomes 'plan' (plan is a kind of arrangement).
'too' placed inside 'plan' is 'PLATOON'.
(Other definitions for platoon that I've seen before include "Sub-unit of a military company" , "detail" , "Military group" , "Group of soldiers" , "Army unit" .)