step-in (st?p??n?)adj. Put on by stepping into: a step-in robe.n.1. step-ins Panties with wide legs.2. A step-in 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.step?-in` adj. 1. (of garments, shoes, etc.) put on by being stepped into. n. 2. step-ins, wide-leg panties for women. [1920?25] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.