Where does “raskasvety” come from?

raskasvety (Finnish) comes from Finnish vety, from Finnish -u, from Proto-Finnic -u — Forms nouns from adjectives, nouns.

Ancestry of “raskasvety”, step by step

raskasvety traces back through two separate lines of ancestry.

via Finnish vety

StepLanguageWordMeaning
1Finnishvetyhydrogen; Indicative present connegative form of...
2Finnish-uForms nouns from verbs. Most common with "e"- and...
3Proto-Finnic-uForms nouns from adjectives, nouns

via Finnish raskas

StepLanguageWordMeaning
1Finnishraskasheavy; hard, laborious, strenuous, gruelling;...
2Proto-Finnicraskasheavy, weighty
Every word from Proto-Finnic -uEvery word from Finnish -uEvery word from Finnish vety