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Plural of Radius
The Quick Answer
The plural of "radius" is "radii" or "radiuses." Both "radii" and "radiuses" are used in the UK and the US. "Radii" is far more common in published writing and academic papers.The Plural of Radius
The plural of "radius" is "radii," but "radiuses" is also used. "Radii" is far more common. The word "radiuses" has only recently (since the 1990s) started to feature in published words.- Calculate the radii of these circles from their circumferences.
- Atomic radii are not precisely defined but are widely in understanding molecular structures.
Are You Good at Plurals?
Here's a quick test.The Standard Rules for Forming the Plurals
The table below shows where "radius" fits within the standard rules for forming the plurals of nouns in English.Type | Example of Type | Forming the Plural | Plural |
---|---|---|---|
Most Nouns | ![]() ![]() |
add s | ![]() ![]() |
Noun Ending s, sh, ch, x or z | ![]() ![]() |
add es | ![]() ![]() |
Nouns ending [consonant] o | ![]() ![]() ![]() |
add either s or es (There are no rules for this - you have to know.) |
![]() ![]() ![]() |
Nouns ending [vowel] o | ![]() ![]() |
add s | ![]() ![]() |
Nouns ending [consonant] y | ![]() ![]() |
change the y to an i and add es | ![]() ![]() |
Nouns ending [vowel] y | ![]() ![]() ![]() |
add s | ![]() ![]() |
Nouns ending f or fe | ![]() ![]() |
ves and/or s (There are no rules - you have to know.) |
![]() ![]() |
Exceptions | ![]() ![]() |
some nouns undergo a vowel or letters change | ![]() ![]() |
More exceptions | ![]() ![]() ![]() |
some nouns do not change at all or adopt a foreign ending (typically Latin) | ![]() ![]() ![]() |
Why Is There Confusion over the Plural of Radius?
"Radius" comes from Latin. It literally means "the spoke of wheel." "Radius" is one of those words that has retained its Latin plural (i.e., "radii"). In English, there are many words that come from Latin, but not all of them have retained their Latin plurals. For example, "referendums" and "syllabuses" (the standard plurals) are far more common than "referenda" and "syllabi" (the Latin plurals).As a result, writers are unsure whether to adopt the standard method for forming the plural of a Latin word or to use the Latin plural.
In the case of "radius," the most common practice by far is to use the Latin plural "radii." [evidence]
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