A bosun's chair (or boatswain's chair) is a device used to suspend a person from a rope to perform work aloft. originally just a short plank or swath of heavy canvas, many modern bosun's chairs incorporate safety devices similar to those found in rock climbing harnesses such as safety clips and additional lines.. Boatswain definition, a warrant officer on a warship, or a petty officer on a merchant vessel, in charge of rigging, anchors, cables, etc. see more.. Hyponyms for boatswain's chair definition for boatswain's chair: a seat consisting of a board and a rope ; used while working aloft or over the side of a ship. Window cleaners cleaning windows of modern office tower Window cleaners cleaning windows of modern office tower ...