Crossword Genius

Ship with a protective inner layer (5)

Ross

I believe the answer is:

liner

'ship' is the definition.
(liner is a kind of ship)

I cannot understand how the remainder of the clue works.

(Other definitions for liner that I've seen before include "Cosmetic; fine paintbrush" , "Large passenger or cargo ship travelling on regular route" , "It covers bin's interior" , "Removable inner skin or large passenger ship" , "QE2, perhaps" .)

I've seen this clue in The Guardian.
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