The most common and most likely answer to this crossword clue is the 6 letter word AVOUCH
A
V
O
U
C
H
Buddy explains!

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 AVOUCH mean?
AVOUCH noun- Evidence; declaration
- To declare freely and openly; to assert.
- To acknowledge deliberately; to admit; to confess; to sanction.
- To confirm or verify, to affirm the validity of.
- To appeal to; to cite or claim as authority.