helluo librorum UK /ˌhɛljʊəʊ lɪˈbɹɔːɹəm/US /ˌhɛljuoʊ lɪˈbɹɔ(ə)ɹəm/ noun1 •(literary, no longer used) An insatiable and obsessive bookworm (“avid book reader”).Among the helluones librorum, the Cormorants of Books, there are wretched Reasoners, that have canine Appetites, and no Digestion. — 1729 formshelluones librorum