The most common and most likely answer to this crossword clue is the 9 letter word FIREBREAK
I've seen this crossword clue in The Times
F
I
R
E
B
R
E
A
K
More clues leading to the result FIREBREAK
Buddy explains!
The straight part
We know that "What might save wood" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what might save wood = firebreak.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 FIREBREAK mean?
FIREBREAK noun- An area cleared of all flammable material to prevent a fire from spreading across it.