The word "字母" is formed through semantic combination, where two meaningful characters are joined to create a new, compound concept. The first character, "字" (zì), means "character" or "written word". The second, "母" (mǔ), literally means "mother" but is used here in a metaphorical sense to signify "source", "origin", or "fundamental unit". Therefore, when combined, "字母" conceptually means "the mother of characters", logically referring to the fundamental symbols, the letters of an alphabet, from which written words are constructed.