Filled is the past participle of fill, from Old English fyllan ('to fill, make full'), from Proto-Germanic *fullijaną, derived from *fullaz ('full'), from Proto-Indo-European *pleh1- ('to fill'). The participial history matters: an older verbal form is preserved as an English adjective or derivative, so the modern word keeps the result of an action as its lexical shape. In present use, it is used as an adjective meaning "made full; occupied or supplied to capacity", so the historical material remains connected with the current sense rather than standing as bare ancestry. The wider English family includes related forms such as fill and full, showing how the same historical material continues to organize neighboring vocabulary. The named historical forms include Old English fyllan and Proto-Indo-European *pleh₁-, keeping the history tied to concrete forms rather than a loose resemblance.