The halo starts before morning, infact covered by sun rise (6)
I believe the answer is:
nimbus
'the halo' is the definition.
(synonyms)
'starts before morning infact covered by sun rise' is the wordplay.
'starts' says to take the initial letters.
'covered by' indicates putting letters inside.
'rise' says the letters should be written backwards.
The initial letters of 'before morning infact' is 'bmi'.
'bmi' put within 'sun' is 'submin'.
'submin' in reverse letter order is 'NIMBUS'.
(Other definitions for nimbus that I've seen before include "round one's head?" , "Large rain cloud; halo" , "Ouse/Trent estuary" , "A rain-cloud or a halo" , "showers under it" .)