Finnish word -kas comes from Proto-Finnic *-k'as

Detailed word origin of -kas

Dictionary entry	Language	Definition
*-k'as	Proto-Finnic (fiu-fin-pro)
-kas	Finnish (fin)	-y, -ful; a suffix that can be used to turn many, but not all, nouns into adjectives that indicate abundant presence of the thing expressed by the noun. When the suffix is added to the noun, the stem changes in accordance with consonant gradation.