Marruttaa

Marruttaa is a Finnish verb meaning to become covered with hoarfrost or frost, or to frost over surfaces. The phenomenon occurs when moist air contacts a surface that is at or below freezing, causing ice crystals to form. The resulting frost layer is typically white and powdery, and it can appear on metal, glass, vegetation, or road edges. The term is common in meteorology, agriculture, horticulture, and everyday weather description.

Etymology and usage notes: The verb is formed from a root associated with frost (kuura or marru) plus the -taa suffix, yielding a verb that describes the action of frost formation or the surface undergoing frost. It is used both intransitively, for surfaces that frost over (marruttuvat), and in colloquial speech with a projected subject.

Usage: In weather descriptions or nature writing, one may say that surfaces frost over. The form is versatile for different tenses: pinnat marruttuvat (the surfaces frost over), pinnat marruttuvat yöllä, or in past tense, pinnat olivat marruttuneet. The participle form marruttunut can describe frost-coated objects, as in “marruttuneet pinnat.”

Examples: Yöllä ikkunat marruttuvat kuurasta. Aamulla pinnat olivat marruttuneet kuurasta. Puut ovat marruttuneet korkeiksi kuuratatuiksi oksiksi.

See also: Frost, hoarfrost, frost formation in meteorology, kuura.