The most common and most likely answer to this crossword clue is the 9 letter word BOMBPROOF
I've seen this crossword clue in The Times
B
O
M
B
P
R
O
O
F
More clues leading to the result BOMBPROOF
Buddy explains!
The straight part
We know that "safe" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case safe = bombproof.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 BOMBPROOF mean?
BOMBPROOF noun- An air-raid shelter, a structure designed to give protection against air raids and bombs.
- To make resistant to bomb blasts.
- Sufficiently strong to resist the effects of a blast from a bomb.