me·tath·e·sis / məˈta[unvoicedth]əsəs/ • n. (pl. -ses / -ˌsēz/ ) 1. Gram. the transposition of sounds or letters in a word.2. (also me·tath·e·sis re·ac·tion) Chem. a reaction in which two compounds exchange ions, typically with precipitation of an insoluble product. Also called double decomposition.DERIVATIVES: met·a·thet·ic / ˌmetəˈ[unvoicedth]etik/ adj.met·a·thet·i·cal / ˌmetə[unvoicedth]etikəl/ adj.

METATHESIS [Stress: ‘me-TA-the-sis’]. The transposition of elements of language, usually two sounds and/or letters in a word: Old English bridd becoming Modern English bird, Middle English Manisk becoming Modern English Manx. Non-standard aks in Don't aks me metathesizes standard ask. Compare SLIP OF THE TONGUE, SPOONERISM.

metathesis XVII. — late L. — Gr. metáthesis, f. metatithénai transpose; see META-, THESIS.
So metathetic XIX.