tween (prep.) Look up tween at Dictionary.com
also 'tween, c.1300 as an abbreviation of between. As a noun meaning "child nearing puberty" (approximately ages 9 to 12), attested by 1988, in this case by influence of teen. Earlier in this sense was subteen (1952). Related: Tweens. Tweeny was a c.1900 term for "a servant who assists two others."