Gag about how paradise is ultimately lost (5)
I believe the answer is:
heave
'gag about' is the definition.
'heave' can be an answer for 'gag' (both can mean to go to throw up). I'm not certain of the 'about' bit.
'paradise is ultimately lost' is the wordplay.
'paradise' becomes 'heaven' (synonyms).
'is ultimately lost' means to remove the last letter.
'heaven' with its final letter removed is 'HEAVE'.
'how' is the link.
Can you help me to learn more?
(Other definitions for heave that I've seen before include "Swell; throw" , "Haul - retch" , "Throw, hurl" , "Throw with force - retch" , "Retch - lift using much effort" .)