1A straight line; figuratively, to go straight toward something (the shortest/direct route or an unwavering focus).
道は一直線に続いている。
The road continues in a straight line.
駅から家までは一直線で歩いて１０分ほどだ。
It's about a ten-minute walk straight from the station to my house.
彼は目標に一直線で努力している。
He is single-mindedly working toward his goal.