"musculo-membranous pouch at the back of the nasal cavities, mouth, and larynx," 1690s, from Greek pharynx (genitive pharyngos) " throat, joint opening of the windpipe," which is related to pharanx "cleft, chasm, gully, deep trench;" all of uncertain origin; Beekes suggests Pre-Greek origin. The combining form is pharyngo-, before vowels pharyng-; the Modern Latin plural is pharynges.
word-forming element in medicine denoting "diseases characterized by inflammation" (of the specified part), Modern Latin, from Greek -itis, feminine of adjectival suffix -ites "pertaining to." Feminine because it was used with an implied nosos "disease," a feminine noun; especially in arthritis (nosos) "(disease) of the joints." Arthritis (16c.) was one of the earliest appearances of the suffix in English and from it the suffix was abstracted in other uses.
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Harper, D. (n.d.). Etymology of pharyngitis. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/pharyngitis