1That occurs or is manifested suddenly, spontaneously, or in haste; sudden, hasty, unexpected.
Of an egg (of certain invertebrates): hatching very soon after being laid, without a period of dormancy. Also: reproducing in this manner; designating or relating to such reproduction.
Mid 17th century. From classical Latin subitāneus sudden (from subitus + -āneus see -aneous) + -ous.