The most common and most likely answer to this crossword clue is the 7 letter word NEGRONI
N
E
G
R
O
N
I
Buddy explains!

The straight part
We know that "Cocktail" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cocktail = negroni.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.
What does NEGRONI mean?
NEGRONI noun- A cocktail consisting of gin, Campari and vermouth.