Disappointment as magician's debut is defined by assorted bad quips (4,5)
I believe the answer is:
damp squib
'disappointment' is the definition.
(a damp squib is something underwhelming)
'magician's debut is defined by assorted bad quips' is the wordplay.
I cannot quite see how this works, but
an anagram of 'quips' is 'psqui' which is located in the answer.
This explanation may well be incorrect...
'as' acts as a link.
Can you help me to learn more?
(Other definitions for damp squib that I've seen before include "Something unsuccessful" , "Firework that doesn't" , "Unsuccessful attempt to impress - firework won't ignite?" , "Anticlimax" , "Let-down" .)