filthy

The word 'filthy' has a direct lineage from Old English, built upon the noun 'filth,' which denoted physical dirt or moral corruption. The core concept of foulness is traceable to a Proto-Germanic root meaning 'to rot' or 'to become putrid,' linking the physical state of decay to a strong sense of moral repugnance. The addition of the productive adjectival suffix '-y' transparently created a term meaning "full of filth." Over time, while retaining its primary sense of extreme dirtiness, its usage expanded in informal contexts to intensify any undesirable quality, such as in 'filthy rich' or 'filthy weather,' leveraging the root's inherent strength to denote excess.

Structure: filth (dirt) + y (adjective-forming suffix) 'filth' originates from Old English 'fȳlþ', meaning foulness or dirt, itself derived from the Germanic root fūlithō, related to fūlaz (foul). The suffix '-y' is from Old English '-ig', a common suffix used to form adjectives from nouns, indicating "characterized by" or "full of."