The word 瓶子 is formed through a process of semantic derivation where the core meaning-bearing character 瓶 (píng), which originally means "vase" or "jar", is combined with the suffix 子 (zi). This suffix 子 does not carry its literal meaning of "child" but functions as a nominalizer, a very common pattern in Mandarin. It attaches to the root to create a freestanding, concrete noun for everyday use, softening the pronunciation and resulting in the common word for "bottle".