The word 窗子 (chuāngzi) is formed by combining the morpheme 窗, a pictographic character historically depicting a window frame with lattice, with the suffix 子 (zi), which is commonly added to nouns in Mandarin to form a familiar, concrete, or everyday term. While 窗 alone means "window", adding 子 doesn't change the core meaning but makes the word more colloquial and disyllabic, fitting the rhythmic and phonetic patterns of modern spoken Chinese. Thus, it is an example of affixation, where a lexical root (窗) is joined with a semantically neutral grammatical particle (子) to create a standard, colloquial noun.