One little nibble reduced puke with some difficulty (2,1,7)
I believe the answer is:
at a stretch
'with some difficulty' is the definition.
(at a stretch means in difficult circumstances)
'one little nibble reduced puke' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'little' means to remove the last letter (the word is not quite complete).
'nibble' becomes 'taste' (I've seen this in another clue).
'reduced puke' becomes 'retch' (synonyms. I am not sure about the 'reduced' bit.).
'taste' with its last letter removed is 'tast'.
'a'+'tast'+'retch'='AT A STRETCH'
Can you help me to learn more?
(Other definitions for at a stretch that I've seen before include "With difficulty; without interruption" , "in one continuous period" , "Running, possibly" , "With much effort" .)