The most common and most likely answer to this crossword clue is the 12 plus 3 letter word DISAPPEARING ACT
I've seen this crossword clue in Financial Times
D
I
S
A
P
P
E
A
R
I
N
G
A
C
T
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.