Fatty Fat"ty, a. Containing fat, or having the qualities of fat; greasy; gross; as, a fatty substance. Fatty acid (Chem.), any one of the paraffin series of monocarbonic acids, as formic acid, acetic, etc.; -- so called because the higher members, as stearic and palmitic acids, occur in the natural fats, and are themselves fatlike substances. Fatty clays. See under Clay. Fatty degeneration (Med.), a diseased condition, in which the oil globules, naturally present in certain organs, are so multiplied as gradually to destroy and replace the efficient parts of these organs. Fatty heart, Fatty liver, etc. (Med.), a heart, liver, etc., which have been the subjects of fatty degeneration or infiltration. Fatty infiltration (Med.), a condition in which there is an excessive accumulation of fat in an organ, without destruction of any essential parts of the latter. Fatty tumor (Med.), a tumor consisting of fatty or adipose tissue; lipoma.