The most common and most likely answer to this crossword clue is the 6 plus 3 plus 5 letter word TICKLE THE FANCY
I've seen this crossword clue in The Guardian
T
I
C
K
L
E
T
H
E
F
A
N
C
Y
Buddy explains!
The straight part
We know that "app/e/al" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case app/e/al = tickle the fancy.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.