Alter al·ter [awl-ter] Show IPA verb (used with object) 1. to make different in some particular, as size, style, course, or the like; modify: to alter a coat; to alter a will; to alter course. 2. to castrate or spay. verb (used without object) 3. to change; become different or modified. Origin: 1350–1400; Middle English < Old French alterer < Late Latin alterāre to change, worsen, derivative of Latin alter other.All Rights Reserved