The most common and most likely answer to this crossword clue is the 27 letter word TASTNIVEERSTASTEVIN/ENVIERS
T
A
S
T
N
I
V
E
E
R
S
T
A
S
T
E
V
I
N
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E
N
V
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S
Buddy explains!
The straight part
We know that "Cup for sampling/are they green?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cup for sampling/are they green? = tastniveerstastevin/enviers.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.