vade mecum vay-dee-MEE-kuhm; vah-dee-MAY-, noun:
1. A book for ready reference; a manual; a handbook.
2. A useful thing that one regularly carries about.
The reader who wants honestly to understand it, and not merely read into it his own ideas, needs some kind of vade mecum to provide the necessary background and explain unfamiliar words and allusions and strange turns of thought. — Robert C. Dentan, “Including Uz and Buz”, New York Times, November 17, 1968
Roget’s Thesaurus, which had come into being as a linguistic example of the Platonic ideal, became instead a vade mecum for the crossword cheat. — Simon Winchester, “Word Imperfect”, The Atlantic, May 2001
Vade mecum is from Latin, literally meaning “go with me.”