place for books, late 14c., from Anglo-French librarie, Old French librairie, librarie "collection of books; bookseller's shop" (14c.), from Latin librarium "book-case, chest for books," and libraria "a bookseller's shop," in Medieval Latin "a library," noun uses of the neuter and fem., respectively, of librarius "concerning books," from Latin librarium "chest for books," from liber (genitive libri) "book, paper, parchment."
Latin liber (from Proto-Italic *lufro-) was originally "the inner bark of trees," and perhaps is from PIE *lubh-ro- "leaf, rind," a derivative of the PIE root *leub(h)- "to strip, to peel" (see leaf (n.)). Comparing Albanian labë "rind, cork;" Lithuanian luobas "bast," Latvian luobas "peel," Russian lub "bast," de Vaan writes that, "for want of a better alternative, we may surmise that liber is cognate with *lubh- and goes back to a PIE word or a European word 'leaf, rind.'"
The equivalent word in most Romance languages survives only in the sense "bookseller's shop" (French libraire, Italian libraria). Old English had bochord, literally "book hoard." As an adjective, Blount (1656) has librarious.