Fifty soldiers involved in transport ordinance (11)
I believe the answer is:
legislation
'ordinance' is the definition.
(thesaurus)
'fifty soldiers involved in transport' is the wordplay.
'fifty' becomes 'L' (Roman numeral).
'soldiers' becomes 'gis' (GI is an informal term for a US soldier).
'involved in' means one lot of letters goes inside another.
'transport' becomes 'elation' (I've seen this before).
'gis' put into 'elation' is 'egislation'.
'l'+'egislation'='LEGISLATION'
(Other definitions for legislation that I've seen before include "Statute law" , "Enacting of laws" , "Passing of bills" , "Group of laws" , "Laws collectively" .)