Having a bulkhead or bulkheads (as in a ship); divided by watertight compartments; also figuratively meaning thick-headed or stubborn.
From 'bulkhead' (a partition in a ship) plus '-ed' to make an adjective. Naval terminology applied both literally to ship construction and figuratively to character traits suggesting stubbornness.
Naval terms often make their way into general English metaphorically—we talk about 'navigating' problems and being 'stuck on the rocks' because centuries of sea trade made sailors' vocabulary everyone's vocabulary.
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