The most common and most likely answer to this crossword clue is the 16 letter word WARM-BLOODEDNESS
I've seen this crossword clue in Independent
W
A
R
M
-
B
L
O
O
D
E
D
N
E
S
S
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.