orlop

English

From Middle English overlop (“deck of a single-decker”), from Middle Low German overlop (“which leaps overhead”). Compare overloop.

orlop (plural orlops)

(nautical) The platform over the hold of a ship that makes up the fourth or lowest deck, hence in full called orlop deck, especially of a warship.
- 1627, Iohn Smith [i.e., John Smith], “How to Build a Ship with the Definitions of All the Principall Names of Euery Part of her Principall Timbers, also How They are Fixed One to Another, and the Reasons of Their Vse”, in A Sea Grammar, with the Plaine Exposition of Smiths Accidence for Young Sea-men, Enlarged. […], London: […] Iohn Haviland, →OCLC, page 5:
  VVhen you haue berthed or brought her [the ship] vp to the planks, vvhich are thoſe thicke timbers vvhich goeth fore and aft on each ſide, vvhereon doth lie the beames of the firſt Orlop, vvhich is the firſt floore to ſupport the plankes doth couer the Hovvle, thoſe are great croſſe timbers, that keepes the ſhip ſides aſunder, the maine beame is euer next the maine maſt, […]

platform over the hold of a ship

Webster's Seventh New Collegiate Dictionary, Springfield, Massachusetts, G.&C. Merriam Co., 1967
Page 12 of The Fortune of War, by Patrick O'Brian
OED 2nd edition 1989
CorPun - Glossary of Royal Navy terms