Piru is a hundreds of years old Finnish word for Devil. Some people think it is kind of a smaller creature than devil but there is a wording for that in use in Finnish language and it is "pikku piru" (little devil). And the word is in every day use in Finland still today.
Meaning is a less strong than synonymous 'Perkele' which is more used like a swear word in Finnish language.
Would be interesting to find out what cave name to Piru Street in Compton, California....
Synonyms of piru are perkele paholainen pelsebuubbi saatana
Used in US as well
"Piru viekoon. Means let the devil take you."