zepto- combining form zep·to- Trending Now: More Trending: lowlife kakistocracy slimeball salacious oligarch SEE ALL See What's Trending Now See More Trending Words What's Trending Now More Trending Words lowlife 'a person of low moral character' kakistocracy 'government by the worst people' slimeball 'a morally repulsive or odious person' salacious 'arousing or appealing to sexual desire' oligarch 'government in which a small group exercises control' SEE ALL Time Traveler! Explore the year a word first appeared Definition of zepto- : one sextillionth (10−21) part of zeptosecond Origin and Etymology of zepto- International Scientific Vocabulary, probably alteration of hepta-; from the fact that 1021 is the seventh power of 103 Seen and Heard What made you want to look up zepto-? Please tell us where you read or heard it (including the quote, if possible). show hide