va·de me·cum 
(vā′dē mēkəm, vä′dē mā-)
(vā′dē mēkəm, vä′dē mā-)n. pl. va·de me·cums
1. A useful thing that one constantly carries about.
2. A book, such as a guidebook, for ready reference.
[Latin vāde mēcum, go with me : vāde, sing. imperative of vādere, to go + mē : ablative sing. of egō, I + cum, with.]