Noun | 1. IX - the cardinal number that is the sum of eight and one9, ennead, Nina from Carolina, nine, ninerdigit, figure - one of the elements that collectively form a system of numeration; "0 and 1 are digits" | Adj. | 1. ix - denoting a quantity consisting of one more than eight and one less than ten9, ninecardinal - being or denoting a numerical quantity but not order; "cardinal numbers" |