Definition of mid-teen in US English:

mid-teen

(also mid-'teen)

noun

  • 1The middle range of a series of years (of a person's age or of a century), temperatures, or monetary values numbered between thirteen and nineteen.

  • 2Specifically. The middle of a person's teenage years.

adjective

  • Of or designating the mid-teens, especially the middle teenage years; (of a person) in the mid-teens.

Origin

1950s; earliest use found in The William and Mary Quarterly. From mid + teen.

Pronunciation

mid-teen

/mɪdˈtiːn/