amphoteros

Greek had a tidy way of saying "the two of them" without counting again. Once a speaker had named two people or things, this word gathered them up and said one thing about the pair at once: the new wine and the new skins are kept safe together, a blind guide and the man he leads fall into the same ditch, Zechariah and Elizabeth were alike upright before God. It is not the plain number "two" (δύο), which counts, and not the sweeping word for "all" (πᾶς), which has no fixed size. It points back at a set the listener already holds in mind and treats it as one.

Paul makes that ordinary word carry an entire argument in Ephesians 2. There the two are not two individuals but two peoples, Jews and Gentiles, named simply as "the two." Christ made the two into one, reconciled the two in a single body, and gave the two one way to the Father. The sentences only work because the word can take two whole parties and hold them as a single quantity that can then be fused.

By the first century the word had also loosened at the edges. Greek letters and contracts of the period use it of groups larger than a pair, and Acts appears to do the same twice: a demon-possessed man overpowers the sons of Sceva, whom Luke has just numbered at seven, and the Pharisees are said to confess "both" of three things the Sadducees deny. Whether Luke really meant more than two in those places is argued. Some hold that only two of the seven sons were present at the beating, and some count the three denials as two ideas, resurrection on one side and angel or spirit on the other.