heteros

This is the everyday use of the word: one more of the same sort. It counts off:

• a second servant
• a second guest
• a second scripture
• a second criminal beside the first

The New Testament writers, and Luke above all, reach for it constantly to keep a story moving from one person or item to the next.

Three shades sit comfortably together here. Sometimes it simply adds one more to an open list ("and another came"). Sometimes it singles out the second of a fixed pair, set against "the one" (you cannot serve two masters: you will love the one and the other). And sometimes, standing alone as a noun, it means the next person over, your fellow, the one you deal with day to day, which is why Paul can say the person who loves the other has fulfilled the law.

What ties these together is that the second item belongs to the same category as the first. The point is not that it differs in nature but that it is a distinct, additional one.

Here the word does more than count. It marks a thing as different in kind, not just one more of the same. A second priest who is not in Aaron's line is a priest of a different order. A second gospel that contradicts the first is not really good news at all. Paul plays on exactly this when he says the Galatians are turning to a different gospel, which is not another, that is, it is so unlike the real thing that it does not even deserve the name.

A close shade of this is the sense of strange or foreign, especially of speech that is not one's own. The disciples at Pentecost spoke in other tongues, languages not their own, and Paul, quoting Isaiah, speaks of God addressing his people through foreign lips.

Readers sometimes assume this different in kind force is always present, but it is not. In plenty of verses the word simply means one more of the same sort (see the first meaning). Context, not the word by itself, decides whether the second thing is merely additional or genuinely of another kind.

In a few places the word marks the next item in a run of days, used much as we say "the next" or "the following." Luke uses it this way in his travel narrative in Acts, where on the next day the ship reaches the next port. It is the ordinary "other" in counting from one day to the day after, narrowed by context to a calendar sequence.