The quality of being in one direction without any turns or curves.
Straightness is usually seen as good because it means things are not complicated or confusing.
Examples:
The ruler shows the straightness of the line.
She checks the straightness of the road.
The straightness of the hallway makes it easy to walk through.
The cat tries to walk with the straightness of a ruler.
The straightness of the river made it easy to follow.
The straightness of the tree trunk was amazing.