Definitions:

1. A Latin phrase meaning "go with me", referring to a handbook, guide, or manual that is regularly carried by a person for easy reference. NOUN
   • The doctor always carries a small medical vade mecum in his pocket for quick reference.
2. Often used to describe a compact, essential book or resource that someone keeps with them for frequent consultation. NOUN
   • Her travel guide became her trusted vade mecum throughout her trip across Europe.

Synonyms:

• guidebook
• handbook
• manual
• reference book