直线用英语说是straight line.
一、straight：
1、释义：
作形容词：直的；直筒型（非紧身）的；准的；正中目标的；平正的；整洁；坦诚的；简单明了的；严肃的，正统的；连续的；纯的；规矩老实的；异性恋的。作副词：直；直接；径直；笔直地；平正地；成直线；立即；正；坦率地；连续不断地。
2、短语：
straight nose挺直的鼻子；second/third straight loss/victory/win二/三连败/胜；second/third straight season/year连续第二/三季度/年；drive straight直线行驶；keep going straight保持直行；look straight直视。
二、line:
1、释义：
线；线条；界线；（尤指运动场地的）场地线，场界；皱纹；褶子；分界线；边线；排；（人）队伍，行列；生产线；按时间顺序排列的人（或物、事件）；字行；台词，对白；话，言语；一段绳（或索、线等）；管道；电话线路；轨道；（行进的）方向，路线；态度。
2、短语：
line up排成一行、站队、排队（等候）；line sb/sth up使站成一队、使排列成一行；line sth up(with sth)使…（与相关的另一物）排齐、使…对齐。
straight line的例句
1、Children always take straight line up to cross the road after school.小孩儿们放学的时候总是排成一条直线过马路。
2、Kindergarten teachers teach children to take straight line up and cross the road safely.幼儿园老师教育小朋友们排成一条直线过马路才安全。
3、Today,I passed by a kindergarten where children were take straight line up to cross the road.Everyone was very cute.今天我路过一家幼儿园，那里的小孩正排队过马路，每个人都很可爱。
4、A ruler can help you draw very perfect straight lines.尺子能够帮助你画出非常完美的直线。
5、Without a ruler,my lines were drawn crookedly.I borrowed a ruler and drew beautiful straight lines.没有直尺，我的线画得歪歪扭扭，我借了一把尺子，画出了好看的直线。