Greasy comes from grease + -y. Grease is from Old French graisse ('fat'), from Vulgar Latin *crassia, from Latin crassus ('thick, fat, dense'). Morphologically, the account is both compositional and suffixal: -y marks the visible structure by which the older base becomes the modern form. In present use, it is used as an adjective meaning "covered with or resembling grease; slippery", so the historical material remains connected with the current sense rather than standing as bare ancestry. The wider English family includes derivatives such as greasily and greasiness and related forms such as grease, showing how the same historical material continues to organize neighboring vocabulary. The named historical forms include Latin crassus, keeping the history tied to concrete forms rather than a loose resemblance. Its semantic neighborhood is marked by oily, fatty, slippery, and slick on one side and contrasts such as dry and clean on the other, locating the modern specialization without adding a new origin story.