The word "十几" is formed through a direct and logical numerical combination: the character "十" (shí), meaning "ten", is joined with "几" (jǐ), which in this context means "a few" or "several". It functions as a single, fused concept where "十" establishes the base decade, and "几" adds an unspecified, small quantity to it, collectively conveying the meaning of "ten-something" or "more than ten but less than twenty".