A staircase or passageway connecting different decks or levels of a ship.
From companion (the cabin on a ship) plus way (a passage). The 'companion' on ships originally referred to the hatchway covering, and over time the word extended to mean the ladder or stairs leading down from it.
Companionways are crucial to ship design—they're built narrow and steep to save space, which is why old sailors had to move carefully below deck. The word preserves maritime history in a single term!
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