Me‐tath″e‐sis (?), n.; pl.Metatheses (�). [L., fr. Gr. μετάθεσισ, fr. μετατιθέναι to place differently, to transpose; μετά beyond, over + τιθέναι to place, set. See Thesis.] 1. (Gram.) Transposition, as of the letters or syllables of a word; as, pistris for pristis; meagre for meager.
2. (Med.) A mere change in place of a morbid substance, without removal from the body.
3. (Chem.) The act, process, or result of exchange, substitution, or replacement of atoms and radicals; thus, by metathesis an acid gives up all or part of its hydrogen, takes on an equivalent amount of a metal or base, and forms a salt.