The word 'windowless' is a transparent modern English compound formed by attaching the native adjectival suffix '-less' to the noun 'window'. The noun 'window' itself has a poetic Scandinavian origin, entering Middle English from Old Norse 'vindauga', meaning 'wind eye', which vividly describes an opening for air and light. The suffix '-less' derives from the Old English adjective '-lēas', meaning 'free from' or 'lacking', which is cognate with the German '-los'. Therefore, the literal construction 'wind-eye-without' logically evolved into the modern descriptive term for an enclosed space devoid of windows.

Structure: window (opening in a wall) + less (without) - window: From Old Norse 'vindauga' (literally 'wind eye'), a compound of 'vindr' (wind) and 'auga' (eye). In this word, it functions as the base noun denoting the architectural feature. - less: From Old English '-lēas', meaning 'devoid of, free from'. It is a productive suffix used to form adjectives meaning 'without (the thing specified)'.