Dawn is nurse misbehaving (7)
I believe the answer is:
sunrise
'dawn' is the definition.
('sunrise' can be a synonym of 'dawn')
'is nurse misbehaving' is the wordplay.
'misbehaving' is an anagram indicator.
'is'+'nurse'='isnurse'
'isnurse' with letters rearranged gives 'SUNRISE'.
(Other definitions for sunrise that I've seen before include "The first light of day" , "everyday occurrence in the East" , "Time of full daylight" , "Day's beginning" , "Tequila --, cocktail" .)