Definition of onesie
1 : a bodysuit for an infant having a snap closure at the crotch and not covering the legs … her husband, Prince William, gratefully accepted a onesie labeled "Daddy's Little Co-Pilot" from a well-wisher …— Michelle Tauber et al.
2 : a one-piece garment for adults usually with long sleeves and pants and sometimes with a hood All eyes were on Pharrell Williams' wife, Helen Lasichanh, during the Met Gala on May 1, but it was for all the wrong reasons. We were hoping Helen would show off her amazing post-baby body after birthing triplets, but instead, she covered her body in a giant red onesie that some Twitter users were comparing to the red Teletubbie!— Christopher Rogers
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