直線 (chokusen) means “straight line” | MotiTan Japanese Dictionary

More examples

定規で直線を引きます。jō gi de choku sen o hi ki ma su

I draw a straight line with a ruler.

地図で二つの町の間の直線距離を調べます。chi zu de futa tsu no machi no aida no choku sen kyo ri o shira be ma su

I check the straight-line distance between the two towns on a map.

Describes a path with one unchanging direction, extending without bends and serving as the shortest route between two points.

二つの点を結び、曲がらずに一定の方向へどこまでも延びる線。futa tsu no ten o musu bi ma ga ra zu ni it tei no hō kō e do ko ma de mo no bi ru sen

Combines 直 (choku, "straight") and 線 (sen, "line"), giving the compound the meaning of a line that does not bend.

In English geometry, a line has no endpoints, while a line segment has two, so this distinction helps explain why a drawn portion of a 直線 (chokusen) is not the whole line.