Just the sort of boat for inland navigation (6)

I believe the answer is:

narrow

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'just' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?

I cannot understand how the rest of the clue works.

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(Other definitions for narrow that I've seen before include "Bigoted opinion" , "With sides close together" , "Slender - spare" , "Strait, of little width" , "Strait or thin" .)

I've seen this clue in the Evening Standard.

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