Shipping hazard; type of lettuce (7)

I believe the answer is:

iceberg

I believe this clue is a double definition.

'shipping hazard' is the first definition.
(I've seen this before)

'type of lettuce' is the second definition.
(I've seen this before)

(Other definitions for iceberg that I've seen before include "threat to ship" , "Unlikely feature of Cos" , "arctic feature" , "Largely hidden danger" , "Variety of lettuce" .)

I've seen this clue in The Telegraph.

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