adjective
(UK, military, nautical, historical) Of a Royal Navy ship of the line in the Napoleonic Era: having at least 100 guns across three gun decks, a complement of 850–875, and weighing approximately 2,500 tons burthen.
(idiomatic) Superb, exceptional; of the best sort; very high quality.
noun
(UK, military, nautical, historical) A first-rate ship of the line.