tween (tw?n)n. A child between middle childhood and adolescence, usually between 8 and 12 years old. Also called tweener.[Blend of teen and between.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.’tween (twin) prep. contraction of between. [1250?1300; Middle English twene, aph. variant of atwene (see a-1) or betwene between] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.