"A polyunsaturated fatty acid present as a glyceride in linseed oil and other oils and essential in the human diet", Mid 19th century: from Latin linum 'flax' + oleic acid.
"A polyunsaturated fatty acid present in animal fats. It is important in metabolism, especially in the synthesis of prostaglandins and leukotrienes, and is an essential constituent of the diet", Early 20th century: arachidonic formed irregularly from arachidic (a saturated fatty acid) from Latin arachis, see arachis oil, + -one + -ic.
