Noun

1. A sudden thought, particularly one that solves a long-standing problem.

   I had been working on the problem for weeks, and then I had a brainstorm and saw that the solution was easy.

2. An unexpected mental error.

Quotations

• 2005: A terrible fielding error from Tony Graffanino proved costly. [...] Aaron Rowand collected an RBI double to get them off the mark before Graffanino's brainstorm. Juan Uribe hit a roller to the second baseman, who let the potential inning-ending double-play ball roll under his glove, leaving runners at first and third bases. Iguchi hit ruins Red Sox's night BBC Online, 5 October 2005

Verb

1. To investigate something, or solve a problem using brainstorming.
2. To participate in a brainstorming session.