adjective: (UK, military, nautical, historical) Of a Royal Navy warship in the Napoleonic Era: having 20–28 guns on one gun deck, a complement of 140–200, and weighing 340–550 tons burthen.
adjective: (idiomatic, uncommon) Terrible, awful; less than fifth-rate.
noun: (UK, military, nautical, historical) A sixth-rate warship.