al·ter (ôl?t?r)v. al·tered, al·ter·ing, al·ters v.tr.1. To change or make different; modify: altered my will.2. To adjust (a garment) for a better fit.3. To castrate or spay (an animal, such as a cat or a dog).v.intr. To change or become different.[Middle English alteren, from Old French alterer, from Medieval Latin alter?re, from Latin alter, other; see al- in Indo-European roots.]al?ter·a·bil?i·ty, al?ter·a·ble·ness n.al?ter·a·ble adj.al?ter·a·bly adv.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.