Non-professional Queen cover (5)
I believe the answer is:
layer
'cover' is the definition.
(thesaurus)
'non-professional queen' is the wordplay.
'non-professional' becomes 'lay' (as in a layman).
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'lay'+'er'='LAYER'
(Other definitions for layer that I've seen before include "Stratum, tier" , "Hen, perhaps" , "Single thickness and hen" , "Film" , "One who does the setting" .)