The story
- Proto-Indo-European*mregʰ-
- Proto-Indo-European*mrógʰ-n̥ ~ *mrégʰ-n̥-s
- Proto-Germanic*bragną
- Proto-West Germanic*bragn
- Old Englishbræġn
- Middle Englishbrayn
- Englishbrain
- Englishstorm
- English todaybrainstorm
From brain + storm. In the sense of "problem-solve", devised as a method of group creative problem-solving by advertising executive Alex F. Osborn and his employees, who coined the term based on the image of using "the brain to storm a problem". First use appears c. 1945. In the sense of "seizure, convulsion, brain activity", from the unrelated idea that it resembles a storm in the brain. First use appears c. 1861.
Etymology from Wiktionary, CC BY-SA 4.0.