Is “stimulus” plural or singular?
The plural of stimulus is stimuli. What’s with the word stimulus, and why does it behave the way it does from its singular to plural form? Keep reading.
The report identified one major stimulus for economic growth.
Researchers studied multiple stimuli to understand the effect on behavior.
The plant responded quickly to the first two stimulus.
They isolated a strong stimuli that caused the reaction.
What the definition of stimulus?
According to the online dictionary, the word stimulus is understood as “something that incites to action or exertion or quickens action, feeling, thought, etc.: The approval of others is a potent stimulus.
What’s the plural of stimulus?
The plural of stimulus (stimuli), is particularly irregular in English: not only does it omit the regular suffix, it changes the spelling of the entire word and, in turn, how it’s pronounced in both singular and plural forms.
This is unusual, even by the already unusual standards set by the English language. Only a few other select nouns in English follow this same pattern: cactus plural is cacti, hippopotamus/hippopotami; octopus: octopi, and so on. See these other nouns that have conserved their Latin form in both singular and plural forms:
Nouns that end in -us/-i
| singular | plural |
| stimulus | stimuli (or stimuluses) |
| cactus | cacti (or cactuses) |
| octopus | octopi (or octopuses) |
| radius | radi (or radiuses) |
| fungus | fungi (or funguses) |
| alumnus | alumni (or almunuses) |
| syllabus | syllabi (or syllabuses) |
The plural of “stimulus,” associate it with “radius” and “stimuli”—they both change the “us” ending to “i” to form their plurals.
Examples of stimulus used in context
1. Congress has passed an unprecedented stimulus package in response to the 2020 coronavirus pandemic in the hopes of stimulating the economy at a time when so many people have lost income due to being out of work.
2. Failing that test was the stimulus I needed to start studying harder.
3. We learned through CrossFit that combining agony and laughter is a powerful stimulus for developing camaraderie. – Major Michael Perry
4. The scaled back stimulus package does not include funding for a second round of $1,200 stimulus checks—a proposal that for months Republican and Democratic leaders supported. (Fortune, 2020.)
5. The second round of stimulus checks would cost around $290 billion—the price tag of the first round of stimulus checks. (Fortune, 2020.)
Examples of stimuli in context:
Sentence examples are from dictionary.com on stimuli/stimulus.
1. “You would expect the same response to the same stimuli,” Hirsch said.
2. Once in school, the children are confronted with a flood of confusing and potentially upsetting stimuli.
3. How a Dutch social-media star and her strange aural stimuli helped combat my chronic insomnia.
4. For example, lack of response to painful stimuli indicates deeper unconsciousness and more severe injury.
5. Should there be another stimulus—the third, after the Bush and first Obama stimuli?
Origin of the word stimulus
From etymonline on stimulus (plural stimuli):
1680s, originally as a medical term, “something that goads a lazy organ” (often the male member), from a modern use of Latin stimulus “a goad, a pointed stick,” figuratively “a sting, a pang; incitement, spur.”
What’s the difference between they’re, their, and there?
Sources
Work Sheet
According to the blog post, what is the primary plural form of “stimulus”?
The post notes that the way “stimulus” forms its plural is irregular because it:
Which of the following words, mentioned in the post, forms its plural similarly to “stimulus”?
According to the Usage Note in the post, which sentence is correct?
The Study Tip suggests associating “stimulus” with “radius” to remember the plural because:
The report identified one major for economic growth.
Researchers studied multiple to understand the effect on behavior.
They isolated a strong that caused the reaction.
The plant responded quickly to the first two .
Similar to “stimulus,” the plural form of “cactus” listed with a conserved Latin form is .
Frequently Asked Questions
What’s the plural of stimulus?
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Yash, D. "What’s the Plural of Stimulus?." Grammarflex, Jun 6, 2025, https://www.grammarflex.com/whats-the-plural-of-stimulus/.
