index li·bro·rum pro·hib·i·to·rum \-līˈbrōrəmprōˌhibəˈtōrəm, -ȯr-\noun (pluralindices librorum prohibitorum) Etymology: New Latin, index of prohibited books 1.sometimes capitalized I&L&P: a list of proscribed books 2.usually capitalized I&L&P: a list of books condemned in whole or in part as dangerous to faith or morals by church authority and forbidden to Roman Catholics — compare index expurgatorius