Rascal assembled dementia equipment (11)
I believe the answer is:
impedimenta
'equipment' is the definition.
(thesaurus)
'rascal assembled dementia' is the wordplay.
'rascal' becomes 'imp' (synonyms).
'assembled' indicates anagramming the letters.
'dementia' anagrammed gives 'edimenta'.
'imp'+'edimenta'='IMPEDIMENTA'
(Other definitions for impedimenta that I've seen before include "baggage etc" , "Military baggage" , "belongings" , "luggage" , "A hindrance" .)