Onttoihin

Onttoihin is a Finnish illative plural form derived from the adjective ontto, which means hollow or empty. In Finnish, the illative case expresses movement into something, and the plural form indicates entering multiple hollows or hollow spaces. Thus onttoihin literally means into hollows. The word is formed by attaching the illative plural suffix -iin to the stem ontto, with the expected phonological adjustments that Finnish applies to consonant clusters and vowels.

The term is mainly a descriptive linguistic example of how adjectives can take case endings to indicate direction and number. It is most commonly encountered in written Finnish, including poetry, literature, or technical discussions of Finnish morphology, rather than in everyday speech. Because ontto describes a physical property (hollow or empty), onttoihin is typically used when referring to entering hollow spaces—such as caves, cavities, or hollowed objects—in a plural or indefinite sense. It can also be used metaphorically to convey entering a void or emptiness in a figurative context.

Etymology links onttoihin to the base adjective ontto and the Finnish illative plural suffix -iin, illustrating a standard pattern in which adjectives derive directional forms through case endings. As with other illative forms, its exact pronunciation and assimilation follow general Finnish phonological rules. See Finnish grammar, illative case, and adjective-noun concord for related concepts.