Straight as opposed to curvy? Jagged or wavy razors seem like an idea that would not have lasted long enough to influence the name. Google is not helping.
Straight as opposed to transverse, like safety razors. It’s a retronym…it didn’t become necessary to add the “straight” until the safety razor, with its transverse blade (perpendicular to the handle) was invented.
In other words, the blade and handle assembly forms an “I” shape rather than a “T” shape.
Straight razors so-called? Hmmmm… gotta ask that. But I know curved ones are called “smiling” razors by many.
This. It was simply a razor, the way putting a stamp on an envelope and dropping it in a box used to be simply “mail.”