ambo

Ambo, ambae, ambo declines exactly like duo, which is to say on the old dual pattern: ambo, ambae, ambo in the nominative, ambos or ambo and ambas in the accusative, amborum, ambarum, amborum in the genitive, ambobus and ambabus in the dative and ablative. There is no singular, for the obvious reason.

The distinction against uterque is real and Roman writers keep it. Ambo means the two taken together, as a pair acting at once; uterque means each of the two separately, and takes a singular verb. Ambo consules venerunt is both consuls arriving together; uterque consul venit is each of them coming, in his own right. Related to ambi-, "around, on both sides", which English has in ambidextrous and ambiguous.