English Words with Unique Plural Forms

Basically, "s" is added to a word to form its plural form, for example, house – houses. Here’s a short list of English words with unique plural form.

• Graffiti are pictographs scratched on walls. Its singular form is graffito.
• Shih Tzu, a breed of dog, has the same plural and singular form.
• Komondor is also a breed of dog. Its plural form is “komondorok”.
• Atlas is the classical term in architecture for the sculpted figure of male used as column to support a superstructure. You might be thinking that its plural form is Atlases, well, it is not. Its plural form is Atlantes.
• Cactus is a green, fleshy, mostly leafless and spiny plant that is endemic to arid regions. This is easy, if you’re answer is cactuses, you are absolutely right. Cacti will be just fine too. Also, the word “focus” plural form is either focuses or foci.
• Alumnus is a male graduate of a college or school. If your answer is alumnuses it’s incorrect, although basically we add –es to words ending in s for their plural form. The correct one is alumni.
• Alumna is a female graduate of a school. Adding s to form its plural is not right because the correct one is alumnae.
• Datum is the singular form of data. Data is sometimes incorrectly stated as datas for its plural form.
• Criterion is a standard by which a judgment can be made; a model or example. If you are thinking that its plural is criterions you are definitely correct though “criteria” is the more accepted and commonly used plural form.
• Ox is a bovine quadruped, as a buffalo or a bison. Oxes is a big no for its plural form but oxen is the correct one.
• Hippopotamus is a large amphibious, short-leg, thick skinned animal. Its plural form is hippopotamuses. Hippopotami will be all right too.
• Equipment and evidence. These words along with others don’t undergo any changes to form their plural forms, they retain their singular form even when use as plural. Other words include deer, moose, vermin, hose, series, sheep and species.
• Sister-in-law’s plural form is sister-in laws but it is more correct to say sisters-in-law.
• Appendix’s plural form could either be appendixes or appendices. The same with index- it could either be indexes or indices.
• Cherub’s (one of the order of angelic beings) plural form is cherubs. “Cherubim” is also correct.

Basic points to remember:

• English nouns regularly form their plurals by adding s or es.
• Most nouns ending in "f" get changed to a "v" and also with an added "es".  (half - halves)
• Nouns ending in y change it to ies if it is preceded by consonant (baby – babies) and s if it is preceded by vowel (donkey- donkeys).