It's heavenly to be dreamy, as if in love (4)
I believe the answer is:
moon
'love' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for moon that I've seen before include "Titan, perhaps" , "down one's pants" , "Expose one's buttocks" , "Heavenly body < exemplified in Titania?" , "Where Armstrong stood" .)