From BiblePortal Wikipedia

Webster's Dictionary [1]

(1): ( n.) The number greater than eighteen by a unit; the sum of ten and nine; nineteen units or objects.

(2): ( n.) A symbol for nineteen units, as 19 or xix.

(3): ( a.) Nine and ten; eighteen and one more; one less than twenty; as, nineteen months.

King James Dictionary [2]

Ni'Neteen, a. Noting the number of nine and ten united as nineteen years.