In the Latin language, it was the custom to do about as we do today; that is, to give a verb a particular meaning by using a preposition along with it.
Thus, with our verb “to walk,” we may say “to walk in,” meaning “to enter”; “to walk up,” meaning “to ascend”; “to walk down,” meaning “to descend,” and so on.
The Romans, however, placed their prepositions before the verb, and usually combined the two words into one. The preposition ambi, which means “around” or “roundabout,” was one of those usually combined. And when combined it was often shortened into amb, or into am, or even changed into amp.
Our English word ambiguous, from the Latin ambiguus, was thus originally formed from the Latin verb ambigo, which came from the two Latin words ambi, roundabout, and ago, to drive. So the verb meant to drive roundabout, or in a wavering or uncertain manner, as a charioteer might drive if he weren’t certain of the road or if the way were indistinct.
At a time when there were few roads it was a common experience to wander hesitantly about the countryside when seeking a strange place, so the verb came to denote any kind of wandering or uncertain moving, and it is thus that ambiguous acquired the meaning “uncertain, vague.”