Fatty comes from 'fat' + the adjectival suffix '-y'. 'Fat' is from Old English 'fǣtt' ('fatted, plump'), originally the past participle of 'fǣtan' ('to cram, load'), of Proto-Germanic origin. Morphologically, the form is compositional, with the named elements combining to produce the modern spelling and sense. In present use, it is used as a adjective and noun meaning "containing or resembling fat; greasy", so the historical material remains connected with the current sense rather than standing as bare ancestry. The wider English family includes derivatives such as fattiness and related forms such as fat, fatten, and fatted, showing how the same historical material continues to organize neighboring vocabulary. The named historical forms include Old English fǣtt, keeping the history tied to concrete forms rather than a loose resemblance. Its semantic neighborhood is marked by greasy, oily, fat, and oleaginous on one side and contrasts such as lean, fat-free, and nonfat on the other, locating the modern specialization without adding a new origin story.