The word 菠萝包 is formed by directly combining the noun 菠萝 (pineapple) with the noun 包 (bun), where 菠萝 acts as a modifier describing 包. This results in a compound noun that names a sweet bun with a crisscrossed, sugary topping visually resembling the texture of a pineapple's skin, hence the literal meaning "pineapple bun".