Salad ingredient hazardous to shipping (7)

I believe the answer is:

iceberg

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

I don't understand the rest of the clue.

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(Other definitions for iceberg that I've seen before include "RMS Titanic's nemesis" , "Calf's parent" , "Titanic breaker" , "Arctic shipping hazard" , "Floating shipping hazard" .)

I've seen this clue in The Daily Express.

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