1
b
: occurring in two distinct forms
dimorphic leaves
sexually dimorphic coloration in birds
2
: combining qualities of two kinds of individuals in one

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Dimorphism varies greatly in the animal kingdom. Among mammals, the male is generally larger than the female, but other differences in appearance tend to be modest. But birds are usually noticeably dimorphic, with the male being the more colorful sex; when we imagine a pheasant, a mallard, a cardinal, or a peacock, we're almost always picturing the male rather than the female. Among spiders the situation is often reversed. The golden orb-weaver spider, for example, is spectacularly dimorphic: the female may be 20 times the size of the male, and she usually ends up eating him, sometimes even while he's mating with her. Many sea creatures, including many fish, take care of gender problems by simply changing from one sex into the other.

Examples of dimorphic in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
The leaves are dimorphic, with the sterile fronds being heart-shaped and the fertile ones resembling arrowheads. Dawn Pettinelli, Hartford Courant, 7 Feb. 2024 Enlarge / Histoplasma capsulatum is a species of parasitic, yeast-like dimorphic fungus that can, if inhaled, cause a type of lung infection called histoplasmosis. Mark Takahashi, Ars Technica, 27 Sep. 2023 However, these behaviors have only been tested in a handful of size dimorphic spiders. Seriously Science, Discover Magazine, 15 Dec. 2017

Word History

First Known Use

1859, in the meaning defined at sense 1a

Time Traveler
The first known use of dimorphic was in 1859

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Cite this Entry

“Dimorphic.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/dimorphic. Accessed 29 Jul. 2026.

Medical Definition

dimorphic

adjective
1
2
: occurring in two distinct forms
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