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English word hellacious comes from English hella, English -acious (Used to form adjectives from nouns.)
hella (English)
(slang, chiefly Northern California) Intensifier, signifies an abundance of a thing; much or many. (slang, chiefly Northern California) Intensifier (modifies verbs); to a large extent; totally; very much.. (slang, chiefly, US) Intensifier (modifies adjectives); to a large degree; extremely; exceedingly. (slang, chiefly Northern California) For sure; totally; hell yeah; used as a strong [...]
-acious (English)
Used to form adjectives from nouns.
hellacious (English)
(slang) Remarkable, unbelievable, unusual.. Horrible, awful, hellish, agonizing. Nasty, repellent.