The most common and most likely answer to this crossword clue is the 8 letter word SUB-ZERO
I've seen this crossword clue in The Guardian
S
U
B
-
Z
E
R
O
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.
What does SUB-ZERO mean?
SUB-ZERO adjective- (of a temperature) below 0°C; freezing cold