incunabulum: [19] An incunabulum is a book printed before 1501. But etymologically the word has nothing to do with books. It comes from the Latin plural noun incūnābula, which had a range of meanings, including ‘swaddling clothes’, ‘cradle’, and ‘infancy’, which point back to its original source, Latin cūnae ‘cradle’. Nineteenth-century antiquarians and bibliographers applied the term to early printed books since they represented the ‘infancy’ of book production.
incunabulum (n.)
1861, singular of incunabula; taken up (originally in German) as a word for any book printed late 15c., in the "infancy" of the printer's art.