The word 箱子 is formed by combining the meaningful character 箱, which originally depicted a bamboo container and means "box" or "chest", with the extremely common and often semantically neutral character 子, which here functions as a nominal suffix. This suffix 子 doesn't add a separate meaning but routinely attaches to single-character nouns to form a standard, comfortable two-syllable word, giving the term a concrete, tangible, and familiar quality, essentially solidifying "箱" into the common, everyday object we understand as a "box" or "suitcase".