The word "straight" as you wrote it does not contain a prefix. A prefix is a letter or group letters added on to the beginning of a word that has a meaning of its own. The word "straight" has no letters added to the beginning of it.
The words you just listed are just that words. The meaning behind it is a mutally agreed definition for the word. If the words were to be switched then nothing else would happen. It would just be a different word used for the same meaning.
Wouldn't it mean that one is gay/homosexual? This meaning that they are clearly NOT "straight" (the frequently used word for heterosexual), because a roundabout (also called a rotary in some areas) is, obviously, NOT straight, but curved.
The word "straight", meaning not bent, is spelt as you have in the question. Ensure that you mean this usage, and not the sense of "narrow waterway", which would be spelt strait (e.g. Strait of Magellan).