Brainstorm: a pun on rainstorm?

Question

The Online Etymology Dictionary unsurprisingly says brainstorm is from the combination of brain and storm.

What I want to know is whether or not this neologism was an intentional pun on the word rainstorm and also whether or not, when people use brainstorm today, they think of it as a pun or an independent word from rainstorm.

I, for one, used brainstorm my entire life without thinking about rainstorm until last week when, as if in a thunderous mental flash, it suddenly occurred to me. Am I just late to make an obvious connection here? Or is this news to other people as well?

Answer 1

The answer appears to be that there is no evidence that brainstorm is a pun on rainstorm. As mentioned in the comments, it was originally used to denote 'a violent transient fit of insanity', and according to Webster, that remains its primary definition.

Elaborating on the transition to its present meaning, Ken Greenwald (Fort Collins, CO - U.S.A.) quotes from the book, America in So Many Words:

BRAINSTORM: Originally a brainstorm was a momentary malfunction of the mind, a ‘cerebral disturbance,’ in the words of an 1894 investigator. A bright idea was not yet ‘a brainstorm’ but a ‘brain wave,’ as far back as “Harper’s” magazine of 1890: ‘Lucilla, with what she was fond of terming a brain wave, comprehended the situation.’ But by the 1920s ‘brain wave’ was subsiding, while ‘brainstorm’ took over the meaning of ‘a sudden surge of ingenuity.’

The first instance of this transferred sense, ‘He had a brainstorm,’ is recorded in the magazine ‘College Humor’ in early 1925. Many brainstorms took place after that, such as this one from 1941: ‘Then I had the brainstorm of getting an English star like Howard to play the part,’ and another from 1993: ‘Then one of the guys working here had a brainstorm.’

As the OP has noted, Etymonline fails to provide any additional insight:

"brilliant idea, mental excitement, fit of mental application," 1849, from brain (n.) + figurative use of storm (n.). As a verb, recorded from 1920s.

It is, however, interesting to note a curious discrepancy in the OED in its native and American English definitions for brainstorming. The former defines it as:

1. British informal a moment in which one is suddenly unable to think clearly or act sensibly: we can only assume that someone simply had a brainstorm and left the important bits out

2. a spontaneous group discussion to produce ideas and ways of solving problems: the participants held a brainstorm

   1. [as modifier]: brainstorm exercises

      North American informal a sudden clever idea: these three brainstorms may flop like other well-intentioned innovations

IOW, the primary and secondary definitions are more or less contradictory. The AE definition also lists both definitions, but in reverse order. Webster similarly lists these contradictory views:

2a : a sudden bright idea

2b : a harebrained idea

(with 1, of course, being about transient fits of insanity.)