One member of a given litter of animal offspring.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "littermate" in a sentence
"Niki and her littermate Viki are the aunt and mother of my late and much lamented disabled cat, Claudius."
"A few moments later he emerged again, carrying an orange-and-white striped kitten that he dropped next to its littermate, also alive and unharmed."
"After moving into my house from an apartment, I decided my orange boy “Doc” needed a playmate so went to the shelter and saw this beautiful 8 week old long haired calico with the most unique marking on her nose like someone took a sharpie and painted her nose black Fell in love immediately, turns out the kitty in the cage with her was her sister/littermate."