Symbol of happiness (8)
I believe the answer is:
bluebird
'symbol of happiness' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for bluebird that I've seen before include "American member of thrush family (seen over Dover?)" , "Name of the cars and boats in which Malcolm and Donald Campbell set land and water speed records" , "Cerulean flier associated with happiness" , "Donald Campbell's speedboat - relative of thrush" , "symbol of happiness" .)