Entry 3 senses · 2 variants Webster, 1913 Nineteen /nīnʹtēn'/ · Nine·teen · IPA /ˈnaɪnˌtin/ a. n. 01 a. Nine and ten; eighteen and one more; one less than twenty; as, nineteen months. 1. Nine and ten; eighteen and one more; one less than twenty; as, nineteen months. 02 n. The number greater than eighteen by a unit; the sum of ten and nine; nineteen units or objects. 1. The number greater than eighteen by a unit; the sum of ten and nine; nineteen units or objects. 2. A symbol for nineteen units, as 19 or xix.