What Is the Plural of Index?
The Quick Answer
The plural of "index" (mathematical) is "indices." The plural of "index" (directory or catalogue) is "indexes."When used to refer to a directory, the noun "index," follows the standard English way of marking the plural and uses -es. The plural is "indexes."
- Indices are a useful way of more simply expressing large numbers. (In mathematics, the plural of index is indices.)
- The NASDAQ Index Directory provides a list of indexes. (The plural of index (a directory) is indexes.)
Are You Good at Plurals?
Here's a quick test.The Standard Rules for Forming the Plurals
The table below shows the standard rules for forming the plurals of nouns in English.Type | Example of Type | Forming the Plural | Plural |
---|---|---|---|
Most Nouns | lamp scythe |
add s | lamps scythes |
Noun Ending s, sh, ch, x or z | index dress |
add es | indexes dresses |
Nouns ending [consonant] o |
zero tomato |
add either s or es (There are no rules for this - you have to know.) |
zeros tomatoes |
Nouns ending [vowel] o | patio ratio |
add s | patios ratios |
Nouns ending [consonant] y | story penny |
change the y to an i and add es | stories pennies |
Nouns ending [vowel] y | donkey chimney |
add s | donkeys chimneys |
Nouns ending f or fe | dwarf hoof |
ves and/or s (There are no rules - you have to know.) |
dwarfs hooves or hoofs |
Nouns ending is | index diagnosis |
change the "is" to "es" | indices diagnoses |
Exceptions | man louse |
some nouns undergo a vowel or letters change | men lice |
More exceptions | salmon sheep |
some nouns do not change at all | salmon sheep |
Foreign rulings | fungus medium |
some nouns adopt foreign rulings | fungi media |
Why Is There Confusion over the Plural of Index?
Confusion arises because the plural of "index" change depending on the meaning of the word.If "index" is used in a mathematical context, the plural is "indices," which has a Latin root.
When used to refer to a directory, the plural of "index" is "indexes," which adheres to the standard rules for forming the plurals of nouns in English.
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