Form; type; affinity.
[Greek tropos, turning.]
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.