tomboy
n. countablen. a girl or woman who likes to play and dress like a boy. She usually enjoys sports and outdoor activities more than traditional 'girly' things.
n. a girl or woman who prefers to play, dress, or behave in a manner typically associated with boys.
She was a tomboy who loved playing soccer with the boys.
Growing up as a tomboy, she spent most of her childhood climbing trees and riding her bike through the neighborhood.
While some viewed her as a tomboy for her preference for hiking boots and baseball caps, she simply felt more comfortable in those clothes than in traditional feminine attire.
From tom + boy. First attested in Ralph Roister Doister (published 1567, written circa 1552), where it is used to describe a boisterous girl; the OED says the citation is however "generally taken" to mean a boisterous boy, and says that a use in The Old Law (published 1656, thought to have been written circa 1599) "certainly" means a boy: "must young court-tits / play tomboys' tricks with her?" By 1579 it was attested in the meaning "an immodest woman", and by no later than 1592 it had developed its modern meaning of a “girl who acts like a boy”.