Definition of: metathesis

(mə·tath′ə·sis) noun plural ·ses (-sēz)
1. The transposition of letters, syllables, or sounds in a word.
2. Chem. A substitution, as the replacing or exchange of one or more radicals or groups in a compound; double decomposition or mutual exchange.
3. Surg. The operation of removing a morbific substance from one place to another for relief, as by pushing a calculus lodged in the urethra back into the bladder.
4. Any change or reversal of conditions. [<LL <Gk. <metatithenai transpose <meta- over + tithenai place]
—met·a·thet·ic (met′ə·thet′ik) or ·i·cal adjective