From Gaulish ambaxtos (“vassal, high-ranking servant”), from Proto-Celtic *ambaxtos (“servant”), from Proto-Indo-European *h₂mbʰi-h₂eǵ- (“drive around”), from *h₂m̥bʰi (“around”) + *h₂eǵ- (“to drive”). See Latin ambigō.
Practice speaking and memorizing "ambactus" and many other words and sentences in Latin.