Eicosatetraenoic acid (ETA) designates any straight chain 20:4 fatty acid.

Two isomers, both of them essential fatty acids, are of particular interest:

Some chemistry sources define 'arachadonic acid' to designate any of the eicosatetraenoic acids. However, almost all writings in biology, medicine and nutrition limit the use the term 'arachidonic acid' to all-cis 5,8,11,14-eicosatetraenoic acid (ω-6).