Gatsby maybe has love for American happiness (3)
I believe the answer is:
joy
'happiness' is the definition.
(I have seen 'Great happiness ' mean 'joy' so perhaps 'happiness' could also mean 'joy')
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for joy that I've seen before include "Rapture" , "Subject of 11 [ODE]" , "Elation" , "Great happiness" , "Intense gladness" .)