A sample reduced vomit, but only just (2,1,7)
I believe the answer is:
at a stretch
'only just' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'a sample reduced vomit but' is the wordplay.
'sample' becomes 'taste' (synonyms).
'reduced' means to remove the last letter.
'vomit but' becomes 'retch' (synonyms. I am not sure about the 'but' bit.).
'taste' with its final letter taken away 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 "Running, possibly" , "in one continuous period" , "With difficulty; without interruption" , "With much effort" .)