1
a
: involuntary orientation by an organism or one of its parts that involves turning or curving by movement or by differential growth and is a positive or negative response to a source of stimulation
b
: a reflex reaction involving a tropism
2
: an innate tendency to react in a definite manner to stimuli
broadly : a natural inclination : propensity
encouraged his tropism toward the theatrical John Updike

-tropism

2 of 2

noun combining form

: tropism
heliotropism

Did you know?

In hydrotropism, a plant's roots grow in the direction of increasing moisture, hoping to obtain water. In phototropism, a plant (or fungus) moves toward light, usually the sun—perhaps because, in the colder climates where such plants are usually found, concentrating the sun's warmth within the sun-seeking flower can create a warm and inviting environment for the insects that fertilize it. In thigmotropism, the organism moves in response to being touched; most climbing plants, for example, put out tiny tendrils that feel around for something solid and then attach themselves or curl around it. When microbiologists talk about tropism, however, they're often referring instead to the way a virus will seek out a particular type of cell to infect. And when intellectuals use the word, they usually mean a tendency shown by a person or group which they themselves might not even be aware of.

Examples of tropism 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.
Noun
The most important mutational changes affect the tissue tropism of the virus – its ability to infect a specific part of the body. Emma Worden-Sapper, The Conversation, 16 Mar. 2023

Word History

Etymology

Noun

generalization of -tropism, after German Tropismus

Noun combining form

-trope or -trop(ic) + -ism, after German -tropismus

First Known Use

Noun

1893, in the meaning defined at sense 1a

Time Traveler
The first known use of tropism was in 1893

Dictionary Entries Near tropism

Cite this Entry

“Tropism.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/tropism. Accessed 17 Feb. 2025.

Kids Definition

: an automatic movement by an organism unable to move about from place to place and especially by a plant that involves a turning or growing toward or away from a stimulus (as light or moisture)
also : a reflex reaction involving such a movement compare taxis

Medical Definition

: involuntary orientation by an organism or one of its parts that involves turning or curving by movement or by differential growth and is a positive or negative response to a source of stimulation
also : a reflex reaction involving a tropism

More from Merriam-Webster on tropism

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!