The most common and most likely answer to this crossword clue is the 7 letter word VOCALIC
I've seen this crossword clue in Financial Times
V
O
C
A
L
I
C
Buddy explains!

The straight part
We know that "to do with vowels" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to do with vowels = vocalic.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 VOCALIC mean?
VOCALIC adjective- Used as a vowel, as opposed to consonantal, especially in Latin.