(1):

(n.) Transposition, as of the letters or syllables of a word; as, pistris for pristis; meagre for meager.

(2):

(n.) 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.

(3):

(n.) A mere change in place of a morbid substance, without removal from the body.