big girl pants

Noun

big-girl pants pl (plural only)

1. (informal, plural, plural-only) Pull-up underwear worn by a girl during and after toilet training, as contrasted to the diapers worn during infancy.
   • Talk about how she'll be able to wear big-girl pants or fancy pants (decorated training pants) because she will learn to use the potty.1987, Stephen W. Garber, Good Behavior: Over 1,200 Sensible Solutions to Your Child's Problems from Birth to Age Twelve, Villard Books, published 1987, →ISBN, page 161
2. (figuratively, informal, plural, plural-only) A notional pair of trousers or underwear worn by a female when acting maturely.
   • I am very disappointed, but we did always say we wanted the best dog for her, so I will have to put my big girl pants on now and have faith that this will be the perfect dog for our family and for Ehlena.2010, Stacy Fry, “Hope for Independence: A Diary Excerpt”, in Kathy Nimmer, editor, Two Plus Four Equals: Celebrating the Partnership of People with Disabilities and Their Assistance Dogs, Dog Ear...

   Antonyms:

   bitchy pants, grumpy pants, scaredy pants