- -itis noun suffix denoting diseases characterized by inflammation, Modern Latin, from Gk. -itis, feminine of adj. suffix -ites "pertaining to." Feminine because it was used with feminine noun nosos "disease," especially in Gk. arthritis (nosos) " (disease) of the joints," which was one of the earliest borrowings into English and from which the suffix was abstracted in other uses.
Etymology dictionary. 2014.