The most common and most likely answer to this crossword clue is the 8 letter word ICE-FREE
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Buddy explains!
The straight part
We know that "safe passage of ships in freezing weather" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case safe passage of ships in freezing weather = ice-free.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 ICE-FREE mean?
ICE-FREE adjective- Free of all ice, not covered in ice.