A term coined by structuralist anthropologist Claude Lévi-Strauss, by analogy with phoneme and morpheme. In his structural analysis of myths, he describes a mytheme as being "a set of items which share a single functional trait", or in other words, a set of items which have one underlying source. It is comparable to Richard Dawkins' term "meme", which he first devised in his book "The Selfish Gene".
Mythemes are organised in binary oppositions, while maintaining one common, unchanging element, as for example a molecule within a compound. Three items in one mytheme according to Lévi-Strauss are:
(a) Cadmos seeking his sister and being ravished by Zeus;
Since Lévi-Strauss invented the term, it has been of some significance in structuralism as well as the theory of narratology.