The most common and most likely answer to this crossword clue is the 6 plus 7 letter word HELLO, GOODBYE
I've seen this crossword clue in The Guardian
H
E
L
L
O
,
G
O
O
D
B
Y
E
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.