Feeling immense joy (8)
I believe the answer is:
ecstatic
'feeling immense joy' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ecstatic that I've seen before include "Cock-a-hoop" , "On cloud nine" , "Cite acts, being overjoyed" , "Overjoyed, over the moon" , "Feeling great rapture or delight" .)