arcsine noun arc·sine \ (ˌ)ärk-ˈsīn \ Trending Now: More Trending: symbiote charlatan lowlife kakistocracy slimeball SEE ALL See What's Trending Now See More Trending Words What's Trending Now More Trending Words symbiote 'an organism living in symbiosis' charlatan 'faker or fraud' lowlife 'a person of low moral character' kakistocracy 'government by the worst people' slimeball 'a morally repulsive or odious person' SEE ALL Time Traveler! Explore the year a word first appeared Definition of arcsine : the inverse function of the sine if y is the sine of θ, then θ is the arcsine of y —abbreviation arcsin First Known Use of arcsine circa 1889 in the meaning defined above See Words from the same year NEW! Time Traveler Seen and Heard What made you want to look up arcsine? Please tell us where you read or heard it (including the quote, if possible). show hide