The most common and most likely answer to this crossword clue is the 6 plus 6 letter word RHESUS MONKEY
R
H
E
S
U
S
M
O
N
K
E
Y
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.