-itis

CIDE DICTIONARY

-itis,  [Gr. 'i`tis, orig, fem. adjective suffix.].

 A suffix used in medical terms to denote an inflammatory disease of; as, arthritis; bronchitis, phrenitis, nephritis.  [1913 Webster]

OXFORD DICTIONARY

-itis, suffix forming nouns, esp.:
1 names of inflammatory diseases (appendicitis; bronchitis).
2 colloq. in extended uses with ref. to conditions compared to diseases (electionitis).

Etymology

Gk -itis, forming fem. of adjectives in -ites (with nosos 'disease' implied)