The most common and most likely answer to this crossword clue is the 2 plus 3 plus 5 plus 4 letter word ET HOC GENUS OMNE
I've seen this crossword clue in The Guardian
E
T
H
O
C
G
E
N
U
S
O
M
N
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.