vademecum

/V AH0 D EY1 M EH1 K AH0 M/
noun
  1. 1

    A referential book such as a handbook or manual.

  2. 2

    A useful object, constantly carried on oneโ€™s person.

Source: https://en.wiktionary.org/wiki/vade%20mecum, https://en.wiktionary.org/wiki/vademecum