What is the origin of “right as rain”?

Question

I looked this up, and came up with:.

It makes no more sense than the variants it has usurped and is clearly just a play on words (though perhaps there’s a lurking idea that rain often comes straight down, in a right line, to use the old sense).

The author here doesn't seem to know very clearly what its origin is. He is speculating it's just a play on words.

Does anyone have any definitive answer or evidence?

Answer 1

Your source World Wide Words makes the point that the phrase right as... has appeared in many forms over the years and that right as rain probably became the favoured variant because of its pleasing alliteration. It seems like a reasonable conclusion and all I can do here is add further support to his theory from an earlier example.

This is from In the Midst of Alarms by Robert Barr, 1894:

"To whom are you engaged? As I understand your talk, it is to Miss Bartlett. Am I right?"

"Right as rain, Renny."

Perhaps it was a phrase that was already in common usage at this point but the triple alliteration here is striking.

Answer 2

The Godzone Dictionary: Of Favourite New Zealand Words and Phrases (2006) says:

The expression right as something has been used in English since medieval times, using a string of comparatives, such as trivet or ninepence. Right as rain emerged in the 19th century and took precedence over all the other forms, possibly because of its pleasing alliteration, and also possibly because rain is perceived as good, and causes growth.

But a book review of the 1955 Dictionary of Early English by Joseph T. Shipley in the June-July 1956 edition of The Crisis magazine says:

Few of us are aware that many commonly used words once had meanings, in many cases, quite the opposite as those now current. Right, in the phrase "as right as rain," originally meant straight in direction.

And The Wordsworth Dictionary of Idioms (1993) agrees. It says as right as rain is:

A pun on the original meaning of right = straight.

The Free Dictionary gives these meanings of right:

adj.
11. Straight; uncurved; direct: a right line.

adv.
2. In a straight line; directly: went right to school.