Affixes

Words in ‑trope are nouns for organisms or objects that exhibit some characteristic whose abstract name ends in ‑tropism or ‑tropy, or for which an adjective exists in ‑tropic. An allotrope is one of two or more different physical forms in which an element can exist, an instance of allotropy; an isotrope (Greek isos, equal) is a substance that is isotropic, having the same composition in every direction; a phototrope is a plant that exhibits phototropism, growth or movement in response to light.

Heliotrope (Greek hēlios, sun) is now the name of a purple-flowered plant, but the term was once applied to various plants whose flowers turn towards the sun, a phenomenon called heliotropism; a lipotrope (Greek lipos, fat) is a substance that has an affinity for lipids and thus prevents excess fat from accumulating in the liver.

The ending also appears in a few names for nineteenth century scientific toys, in which the ending has the literal sense of ‘turning’: thaumatrope (Greek thauma, marvel), a disc with pictures on its sides, which appear to combine into one when the disc is spun; zoetrope (Greek zōē, life), a cylinder with a series of pictures on the inner surface that give an impression of continuous motion when viewed through slits with the cylinder rotating.