名詞 diameter:

1. the length of a straight line passing through the center of a circle and connecting two points on the circumference
   同義詞：diam
2. a straight line connecting the center of a circle with two points on its perimeter (or the center of a sphere with two points on its surface)

1. The axis of a circle is its diameter.
   圓的軸線是其直徑。
2. We must gauge the diameter of wire first.
   我們必須先測量電線的直徑。
3. The diameter of the tree-trunk is about 2 meters.
   這樹干的直徑大約是2米。
4. This lens can magnify 20 diameter.
   這個透鏡能放大20倍。

di.am.e.ter

n.（名詞）
Abbr. dia.,diam.Mathematics
縮寫 dia.,diam.【數學】
A straight line segment passing through the center of a figure, especially of a circle or sphere, and terminating at the periphery.
直徑：穿過一圖形，特別是圓形或球形的中心到圓周結束的直線段
The length of such a segment.
直徑長：這樣一段的長度
Thickness or width.
厚度或寬度

來源：
Middle English diametre
中古英語 diametre
from Old French
源自 古法語
from Latin diametrus
源自 拉丁語 diametrus
from Greek diametros
源自 希臘語 diametros
dia- [dia-]
dia- [前綴，表.完全的，有始有終的.]
metron [measure] * see mô- 2
metron [測量] *參見 mô- 2

【引伸】
diam.etral