1. In biochemistry, an unsaturated acid, obtained from lecithin; a fatty acid essential for growth of mammals, but which can be synthesized from linoleic acid; from Arachis, a generic name for the peanut.
2. Arachidonic acid is found only in animal fats, as in egg yolk and liver.
3. Coined from the modern Latin stem arachid-, "peanut" (from Greek arakhos, "a type of leguminous plant").