grasa

The root noun is graso, fat as a substance - the stuff in the pan, the layer on the meat, the content of the milk. Grasa is the adjective from it, so it describes things that contain or are covered in fat: grasa viando, grasa supo, grasaj manoj, grasa haŭto.

It is not the polite word for a fat person. For that, Esperanto uses dika, which means thick or stout and is the ordinary, unloaded description; dikulo is a stout person. Grasa homo reads as greasy rather than stout, which is a good deal ruder than the speaker usually intends. This is the sort of mistranslation that produces a genuinely unpleasant sentence out of a perfectly innocent English one, so it is worth fixing before it happens.

Two more senses worth carrying. In typography grasa means bold: grasa litero is a bold letter, grasa tiparo a bold typeface, and this is standard in Esperanto publishing. And grasigi means to fatten (an animal), while malgrasa is lean or thin, the word a butcher uses about a cut of meat.