The most common and most likely answer to this crossword clue is the 17 letter word PENNY-IN-THE-SLOT
I've seen this crossword clue in Financial Times
P
E
N
N
Y
-
I
N
-
T
H
E
-
S
L
O
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.