Q:

Is there a word to call the second rainbow above the first?

As is known, a double rainbow is formed when there are two reflections inside a raindrop and a second rainbow, which tends to be fainter than the first, is distinguishable above the first.
Since in 'Shakespeare's Non-Standard English: A Dictionary of His Informal Language' by Norman Blake I found that, as an instance, 'water-gall' means 'small rainbow which at sea precede a storm', I began to wonder whether there is also a word to call that second rainbow. Is there?
Yes, I know that second rainbow or secondary rainbow or even faint rainbow can be used, but I'm looking for an informal or slangy name.

A:

The specific one OP is talking about is called the secondary rainbow (as opposed to the primary).
There can be more than two. All except the primary are loosely called "supernumerary" rainbows, but supernumerary/stacker rainbow is also a specialised term for multiple bows appearing inside the primary, which are caused by lightwave interference rather than reflection by water droplets.

A:

It's usually called a double rainbow in the US.
Although I misunderstood the question originally (I did not realize that you were looking for a specific piece of a rainbow), apparently, the actual scientific term for the primary and secondary rainbows are just that, as explained by this guide.

