toth·er or t’oth·er (t?th??r)pron. & adj. Informal The other.[From Middle English the tother, alteration of thet other, that other : thet, the (from Old English thæt; see that) + other, other; see other.]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.