What is the plural form of the word 'Radius'?

♦ Radius:
English meaning: a line segment extending from the center of a circle or sphere to the circumference or bounding surface.
Bangla meaning: ব্যাসার্ধ।
Plural form: Radii.

• কিছু কিছু noun এর plural অনিয়মিতভাবে হয়ে থাকে। যেমন:

• Singular: plural
- Agendum: Agenda
- Crisis: Crises
- Radius: Radii
- Thesis: Theses
- Medium: Media etc.

Source: A Passage to the English Language by S.M. Zakir Hussain.