The word "一会儿" is formed through the fusion of the numeral "一" (yī, meaning "one") with the colloquial temporal measure word "会儿" (huìr), which itself is a contraction of "会" (huì, implying a meeting or convergence of time) and the erhua suffix "儿" (r), a northern Mandarin feature that often conveys a sense of smallness or informality. This combination structurally creates a single, indivisible unit that conceptually quantifies a short, indefinite period, literally "one small gathering/segment of time", with the erhua suffix softening and colloquializing the expression into its modern, fixed form meaning "a little while".