in Molière's Malade Ìmaginaire. A man of fossilised ideas, who, like the monk, refused to change his time-honoured mumpsimus (q.v.), for the new-fangled sumpsimus. Dr. Diafoirus used to say, what was good enough for his forefathers was good enough for their posterity, and he had no patience with the modern fads about the rotundity of the earth, its motion round the sun, the circulation of the blood, and all such stuff.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894