c.1400 (mid-14c. as Anglo-French forechasteil), "short raised deck in the fore part of the ship used in warfare," from Middle English fore- "before" + Anglo-French castel "fortified tower" (see castle, n.). In broader reference to the part of a vessel forward of the fore rigging, late 15c.; hence, generally, "section of a ship where the sailors live" (by 1840). Spelling fo'c'sle reflects sailors' pronunciation.