Straight
From the Simple English Wikipedia, the free encyclopedia that anyone can change
The word straight means something that goes in one direction without turns, bends, or curves.
Lines can bend in a curve. If lines do not bend, they are straight. For example, the edge of a circle is not straight. The edge of a circle bends in a curve.
Light bends in a curve in air and water, but travels in a straight line away from the earth or other bodies in space where there is no air.
In slang, just as the word gay means homosexual, the word straight means heterosexual.