1. (Science: chemistry) The property of crystallizing in three forms fundamentally distinct, as is the case with titanium dioxide, which crystallizes in the forms of rutile, octahedrite, and brookite. See pleomorphism.
2. (Science: biology) The coexistence among individuals of the same species of three distinct forms, not connected, as a rule, by intermediate gradations; the condition among individuals of the same species of having three different shapes or proportions of corresponding parts; contrasted with polymorphism, and dimorphism.
(Science: botany) heterogonous trimporphism, that condition in which flowers of plants of the same species have three different lengths of stamens, short, medium, and long, the blossoms of one individual plant having short and medium stamens and a long style, those of another having short and long stamens and a style of medium length, and those of a third having medium and long stamens and a short style, the style of each blossom thus being of a length not represented by its stamens.