a book of special value or interest on account of its age, limited issue, binding, or other historical factors; frequently attributive.
With plural agreement. Rare books.
With plural agreement. Curiosities, oddities; spec. erotic or pornographic books (cf. curious, adj. 16b).
With plural agreement. Extremely rare books, manuscripts, or prints.
Unfindable, undiscoverable; spec. of books. Also as n.