Quiz: Grammar Do You Know The Plural Forms Of The 15 Trickiest Words In English

The standard English plural is 'octopuses', though 'octopodes' is sometimes used from the Greek root. 'Octopi' is a common but incorrect Latinization because octopus is Greek, not Latin. Most dictionaries list 'octopuses' as the primary plural.

Cactus comes from Latin, so the Latin plural 'cacti' is traditional, though 'cactuses' is also acceptable in English. 'Cactii' is never correct.

Fungus is a Latin second-declension noun, so the correct plural is 'fungi'. 'Funguses' is sometimes used but less common, and 'fungii' is incorrect.

Nucleus follows the Latin pattern: the plural is 'nuclei'. 'Nucleuses' is occasionally used but considered less standard.

While both 'syllabuses' and 'syllabi' are accepted, 'syllabi' follows the Latin pattern of the word's origin, and is common in academic contexts.

Words ending in -is change to -es: analysis becomes analyses. This follows the Greek pattern (e.g., crisis → crises, thesis → theses).

Crisis follows the same Greek pattern as analysis: the -is becomes -es, giving 'crises'.

Like analysis and crisis, thesis becomes theses by changing -is to -es.

Criterion is a Greek neuter noun; the standard plural is 'criteria'. 'Criterions' is sometimes used but is nonstandard.

Phenomenon is Greek, so its plural is 'phenomena'. 'Phenomenons' is used in informal contexts, but the standard plural is phenomena.

For a book, 'appendices' is standard; in medical contexts 'appendixes' is also used, but 'appendices' is the traditional Latin plural.

In mathematics, 'indices' is common; in general English, both 'indexes' and 'indices' are accepted, but 'indices' is the Latin plural.

Matrix is Latin, so the plural is 'matrices' (or sometimes 'matrixes' in informal contexts, but matrices is preferred).

Ellipsis, like analysis, comes from Greek and changes -is to -es: ellipses.

Vertebra is a Latin feminine noun; the plural is 'vertebrae' (or sometimes 'vertebras' in English, but vertebrae is preferred in formal writing).