1701, "quality or condition of being inaccurate," from inaccurate + abstract noun suffix -cy. As "an instance of being inaccurate, that which is inaccurate," 1704.
"not exact or correct," 1690s, from in- (1) "not" + accurate. Unaccurate is attested from 1670s. Related: Inaccurately (1660s).