One·sies (w?n?z?z?) A trademark for a brand of one-piece garments for infants. This trademark, often styled without a final s and in lowercase, sometimes occurs in print with the meaning “a one-piece infant’s garment.”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.