Definition of round-down in US English:

round-down

noun

Nautical
  • 1Shipbuilding. A camber in any of the timbers of a sailing ship, especially in the beams of the deck from one side of the ship to the other.

  • 2A section of the flight deck of an aircraft carrier (originally at the aft, but later also forward), shaped to reduce air turbulence on the deck and facilitate landing.

Origin

Early 19th century. From round + down. Compare earlier round-aft, roundup.

Pronunciation

round-down

/ˈraʊndˌdaʊn/