The word 'unfilled' is a straightforward English formation built from native Germanic elements. The core verb 'fill' derives from the Proto-Germanic fullijaną, meaning "to make full," which itself is connected to the adjective fullaz (full). The Old English negative prefix un-, one of the most common and productive in the language, is added to negate the state. The participial suffix -ed is then attached, converting the verbal idea into an adjective describing a state—specifically, the state of not having been made full. The logic is transparent: something that is 'unfilled' has not undergone the action of filling, leaving it empty or vacant.

Structure: un (not) + fill (to make full) + ed (adjective suffix) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative or reversing particle. - fill: A verb of Germanic origin (Old English fyllan), meaning "to make full." It functions as the core lexical root. - ed: A suffix of Germanic origin (Old English -ed, -od), originally forming the past tense and past participle of verbs, here used to create a participial adjective.