Deity to be celebrated with event coming round (3,3)
I believe the answer is:
sun god
'deity' is the definition.
(sun-god is a kind of deity)
'be celebrated with event coming round' is the wordplay.
'be celebrated' becomes 'sung' (as opposed to 'unsung').
'with' says to put letters next to each other.
'event' becomes 'do' (do is a kind of event).
'coming round' shows that the letters should be reversed in order.
'do' written backwards gives 'od'.
'sung'+'od'='SUN-GOD'
'to' acts as a link.
(Other definitions for sun god that I've seen before include "RA" , "Amen-Ra" .)