incunabulum n.

1824, a Latin word meaning "swaddling clothes," also, figuratively, "childhood, beginnings, birthplace, place where a thing had its earliest development, the beginning of anything;" especially "early printed book using movable-type technology," From Gutenberg's beginning c. 1439 to the close of the year 1500. Latin incunabula "a cradle; a birthplace," figuratively "rudiments or beginnings," is from in "in" (from PIE root *en "in") + cunabula, diminutive of cunae "cradle," from PIE *koi-na-, suffixed form of root *kei- (1) "to lie," also forming words for "bed, couch."

Interest in collecting them began c. 1640 with the celebration of (as it was supposed) the 200th anniversary of printing. Perhaps this use of the word traces to the title of the first catalog of such books, Incunabula typographiae (Amsterdam, 1688). The word in this sense has come into general use throughout Europe. The number of books put on the market throughout Europe during that period has been estimated at 20 million. Prof. Alfred W. Pollard [Encyclopaedia Britannica, 1941] wrote that "up to the end of the 17th century," Caxton's original printings "could still be bought for a few shillings."