diameter [daɪ'æmɪtə] n. 直径

eg: Atlas, the flatter of the two, has a diameter of only 18 kilometres from pole to pole, but is almost 40 kilometres across its waist.
阿特拉斯是两者中较平整的一个，从南极点到北极点的直径只有18公里，但是它的赤道周长却有40公里。