A list of persons or things out of favor, as in Tom's in my black book these days. This usage dates from the 14th century and in time became more ominous. In 1536 the agents of King Henry VIII wrote in a black book the names of those to be censured or punished, specifically “sinful” English monasteries (whose lands Henry wanted to acquire). Today being in someone's black book still signifies being in trouble, at least with that person. Also see black list.

Also, little black book. A personal telephone directory listing girlfriends, or, less often, boyfriends. For example, Now that he's engaged to Ellen, Jim won't be needing his little black book. [1930s]

A list of measures or facts involved in the unfriendly takeover of one company by another. This usage is employed mainly in business and commerce. [c. 1980]