One having three lines listened to stoned fancy (5)
I believe the answer is:
haiku
'one having three lines listened to stoned fancy' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
This is all the clue.
Can you help me to learn more?
(Other definitions for haiku that I've seen before include "Japanese 3-line poem of 17 syllables" , "Jap 17-syllable poem" , "ode" , "Epigrammatic verse" , "Japanese form of poem" .)