Crossword Genius

In the main submarine hazards (8)

Ross

I believe the answer is:

icebergs

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'hazards' is the definition.
Although both the answer and definition are plural nouns, I can't understand how they can define each other.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for icebergs that I've seen before include "Huge masses of frozen water" , "Large masses of frozen water" , "Frozen mountains in the sea" , "Large masses floating at sea in polar regions" , "Large masses of floating ice" .)

I've seen this clue in The Globe and Mail.
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