The diameter of a circle is a straight line from one side to the other that goes through the centre. People also use the word for how long that line is: the diameter is ten centimetres.

The diameter一個圓的直徑 of a circle is a straight line是一條直線 from one side to the other從一邊到另一邊 that goes through the centre通過圓心。People人們 also use the word也用這個字 for how long that line is指那條線有多長: the diameter直徑 is ten centimetres是十公分。

You meet it first in maths, then on pipes, plates, coins, wheels, and trees — anything round enough that “how wide through the middle?” is a useful question. Though actually, a tree trunk is not a perfect circle, but people still say its diameter, meaning the width through the middle.

You你 meet it first最先遇到它 in maths在數學課, then後來 on pipes, plates, coins, wheels, and trees在管子、盤子、硬幣、輪子、和樹上 — anything round enough任何夠圓的東西 that "how wide through the middle?" is a useful question讓「中間有多寬？」變成一個有用的問題。Though actually但其實, a tree trunk一棵樹幹 is not a perfect circle不是完美的圓形, but但 people人們 still say其實仍然說 its diameter它的直徑, meaning指的是 the width through the middle穿過中間的寬度。

The short line from the centre out to the edge is the radius; the diameter is twice as long.

The short line那條短線 from the centre out to the edge從圓心到邊緣 is the radius叫做半徑; the diameter直徑 is twice as long是半徑的兩倍長。

It is a classroom and measuring word, not a chatty one, but anyone who has put a ruler across a round thing has used the idea.

It它 is a classroom and measuring word是課堂和測量用的字, not a chatty one不是聊天用的字, but但 anyone任何人 who has put a ruler across a round thing曾經把尺放在圓形物體上量過的人 has used the idea都用過這個概念。