The most common and most likely answer to this crossword clue is the 6 letter word PETERS
P
E
T
E
R
S
More clues leading to the result PETERS
Buddy explains!

The straight part
We know that "safe, safe" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case safe, safe = peters.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 PETERS mean?
PETERS verb- In whist, to play a blue peter.
- The penis.
- A safe.
- (most often used in the phrase peter out) To dwindle; to trail off; to diminish to nothing.