Sloops, ketches, and yawls have triangular-shaped sails.
Square sails (rectangular) were (are) called four-cornered sails.
Trapezoidal, actually. But the square sails were called square sails. Lateen or square could be referred to as yards.
"Square-riggers" have primarily square sails, but the jib sails are triangular.
Square sails are square
They were referred to as "four-cornered" sails.
Square sails are not truly square but rectangular with a longer long side on the bottom perimeter of the sail. They were and are referred to as "four-cornered" sails.
The boat had triangular sails.
foremost sail has triangular shape
Those boats were Dhows.
The boat was small and had two triangular sails.
it is called a flying jib