1. the number equivalent to the product of three and ten; ten less than forty; 30: "thirty or forty years ago"
▪ the numbers from thirty to thirty-nine, especially the years of a century or of a person's life: "a woman in her thirties"
▪ thirty years old: "I've got a long way to go before I'm thirty"
▪ thirty miles an hour: "doing about thirty"
▪ a size of garment or other merchandise denoted by thirty.
▪ the second point won by a player in a game:"with the score at thirty all Kumar hit a low volley into the net"
Word OriginOld Englishthrītig (see three, -ty2). The spelling with initial thi- is recorded in literature in the 15th century, and has been the prevalent form since the 16th century.