Finnish word varoitin comes from Finnish -in, Finnish varoittaa ((transitive) To warn; to forewarn.)

Detailed word origin of varoitin

Dictionary entry	Language	Definition
-in	Finnish (fin)	Suffix variant for the illative singular, see -Vn. Instructive case suffix. (poetic) A variant for the first-person singular possessive suffix -ni. (rare) Forms the genitive plural. Forms superlative adjectives. Forms inanimate instrumental nouns from verbs.
varoittaa	Finnish (fin)	(transitive) To warn; to forewarn.
varoitin	Finnish (fin)	Any device that is designed to give a warning, a beacon or an alarm.

Words with the same origin as varoitin