The most common and most likely answer to this crossword clue is the 7 letter word ANTONIO
I've seen this crossword clue in The Guardian
A
N
T
O
N
I
O
More clues leading to the result ANTONIO
- Merchant advanced weird notion
- Merchant displaying a set of books on Galilean satellite
- Worker on Iago, heartless character in Shakespeare
- In Hunstanton I organised The Merchant of Venice
- Not tense at first, prepared notation for The Merchant of Venice
- Vivaldi’s first sonata ending in ‘not moved by love’
- 7’s 24 1 8 5 17 after 18, one hundred and ten?
- Merchant? One such with onions includes me
- American not in play at the Globe
- A Winter’s Tale character I love after soon rescuing protagonist at the end
Buddy explains!
The straight part
We know that "Vivaldi’s first" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vivaldi’s first = antonio.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.