vade mecum

This is a metaphor, borrowed partly from the grazier's vocabulary, and partly from the arithmetician's vade-mecum.

The bow at that time was his vade-mecum; he never left it home.

The passage in The Rhetorician's Vade-mecum is the chief authority for their style.

This excellent handbook will prove a perfect Vade-mecum to those engaged in the practical work of Mining and Metallurgy.