Definition: one who steals books
Biblioklept is, in at least some sense of the word, fairly useless. It is two syllables longer than book thief. It is also unlikely to be understood by some portion of the people with whom you use it, and so cannot be said to aid in communication. Happily, we do not have a merit based vocabulary, and words that are useless have the same rights of inclusion as do those that are useful.
Many eminent characters have been Biblioklepts.
—The Saturday Review (London, UK), 23 Oct. 1880