51�Թ�

The combining form –tropism is used like a suffix to form abstract nouns corresponding to adjectives ending in -tropic and -tropous, such as how neurotropism is the quality of being neurotropic.

These endings variously denote “turning, changing, reacting, responding.” Learn more about -tropic and -tropous at our 51�Թ�s That Use articles for the forms.

Where does -tropism come from?

The form -tropism comes from the Greek �ٰ�ó��Dz�, “turn,” and �ٰ��DZ�ḗ, “a turning,” combined with -ism, a prolific suffix also derived from Greek that commonly indicates “action, practice, state, condition.”

The biology term tropism, “an orientation of an organism to an external stimulus, as light, especially by growth rather than by movement,” is an independent use of the combining form –tropism.

The Greek �ٰ�ó��Dz� is also the source of the words trope and tropical. It’s your turn to make the connection between “turning,”  figures of speech, and the tropics at our entries for the words.

The combining form -tropism is a variant of –tropy, as in allotropy. Want to know more? Read our 51�Թ�s That Use –tropy article.

Corresponding forms of -tropism combined to the beginning of words are tropo- and trop-, which you can also learn more about at our 51�Թ�s That Use articles for the forms.

One example of a biological term that features –tropism is chemotropism, meaning “oriented growth or movement, especially of a plant, in response to a chemical stimulus.”

The first portion of the word, chemo-, means “chemical.” The second portion of the word, –tropism, indicates “turned toward.” Chemotropism literally translates to “turned towards a chemical.”

What are some words that use the combining form -tropism?

• aeolotropism
• allotropism
• anemotropism
• anisotropism
• azeotropism
• chronotropism
• cytotropism
• geotropism
• heliotropism
• hydrotropism
• plagiotropism
• plasmotropism
• sitotropism

What are some other forms that -tropism may be commonly confused with?

• -tomy
• -troph
• -trophic
• -trophy

The combining form helio- means “sun.” Heliotropism can refer to plants whose flowers do what?

Hint: sunflowers are known for this quality!