Around 2,300 BC
"Square-riggers" have primarily square sails, but the jib sails are triangular.
Sloops, ketches, and yawls have triangular-shaped sails.
Square sails are square
They were referred to as "four-cornered" sails.
The boat had triangular sails.
Square sails (rectangular) were (are) called four-cornered sails.
The boat was small and had two triangular sails.
caravel
caravel
Trapezoidal, actually. But the square sails were called square sails. Lateen or square could be referred to as yards.
Either a marconi or lanteen rig