The compound adjective "three-button" is a modern English formation that transparently combines the cardinal number "three" with the noun "button." The word "three" descends from the Proto-Indo-European root trei-, which gave rise to the numeral across many Indo-European languages, signifying its fundamental conceptual nature. "Button" has a more tactile history, originating from a Germanic root meaning "to thrust or strike," which evolved in Old French to denote a bud or knob, and later the fastener that is pushed through a slit. The compound's logic is purely descriptive, directly specifying a garment feature by counting its fasteners, showcasing English's productive capacity for creating precise, compound modifiers.

Structure: three (number) + button (fastener) - three: From Old English þrīe, þrēo, of Germanic origin; related to Dutch drie and German drei, from an Indo-European root shared by Latin tres and Greek treis. Functions as a cardinal number. - button: From Old French boton, from boter 'to butt, thrust', of Germanic origin. Functions as a noun denoting a small fastener.