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

The plural form of the word 'radius' is 'radii.' This form comes from Latin, where many scientific and mathematical terms derive their roots. In Latin, 'radius' translates to 'ray' or 'spoke,' and when pluralized, it follows the convention of changing the ending -us to -i, which is common for masculine nouns in Latin.

This derivation is crucial in various fields, especially in mathematics and physics, where terms derived from Latin are frequently employed. Understanding the correct pluralization not only enhances language use but also aids in clear communication within technical contexts. Choices that suggest alternative forms do not follow the established conventions of Latin-based pluralization, leading to their inappropriateness in formal use.