Hallucination is no end of nonsense (4)
I believe the answer is:
trip
'hallucination' is the definition.
(trip is a kind of hallucination)
'no end of nonsense' is the wordplay.
'no end of' means to remove the last letter.
'nonsense' becomes 'tripe' (I've seen this before).
'tripe' with its final letter taken away is 'TRIP'.
'is' is the link.
(Other definitions for trip that I've seen before include "holiday" , "Accidental misstep" , "Journey, excursion" , "Jaunt" , "Journey; make a mistake" .)