physical form of a chemical element that has distinct properties, or the existence of such forms; for example, graphite and diamond are both allotropes of carbon

a mass of protoplasm characteristic of certain stages in the life cycle of slime molds

An organism, substance, or linguistic form that shares the same shape, structure, or written form as another; (linguistics) homograph

a chemical substance or mineral that shares the same crystalline structure and form as another substance despite having a different chemical composition