An American Slang word meaning 'large,' 'many,' 'super', or 'very.' It is becoming a generic superlative, and there are a surprising number of products with mondo in their name (Mondo "DIVETEX" diving boards, Mad River Mondo Bond Adhesive, the Mondo Snare drum, MONDO Publishing, Mondo Motors diecast cars, to take a radom handfull).
It almost certainly comes from the Italian word Mondo, meaning 'world.'
It most likely entered the English language by way of the 1961 shockumentary film entitled Mondo Cane (meaning, roughly, A Dog's life, or more literally "world for a dog"). The film was rather extreme in tone, with nudity!, murderous witches and a smoking chicken. Hence the usage of 'mondo' to mean extreme (in various forms) may come from a misuderstanding of this title.
Mondo is often seen in the phrase Mondo Bizarro.
Thanks to sid for ier help and clarification.