Why is the ninth month called September?
"teen-aged person," 1818 (but rare before 20c.), from -teen. As an adjective meaning "of or for teen-agers," from 1947.
combining form meaning "ten more than," from Old English -tene, -tiene, from Proto-Germanic *tekhuniz (cf. Old Saxon -tein, Dutch -tien, Old High German -zehan, German -zehn, Gothic -taihun), an inflected form of the root of ten; cognate with Latin -decim (cf. Italian -dici, Spanish -ce, French -ze). The combining form of ordinal numbers, -teenth, developed from Old English -teoða, -teoðe (West Saxon), teogoða (Anglian) "tenth."
A teenage person; teenager: a really interesting biz for a teen who loves being busy/ a robust health that would be remarkable on a teener/ ''You only pass this way once,'' he tells a teenie in persuading her to come along for a ride