I just read a definition that I found interesting, not because I didn't know what the word meant but for the history and spelling of it. This word goes through my mind every time I go to certain threads on GD and GDP.
"hare·brained (hâr'brānd')
adj. Foolish; flighty: a harebrained scheme."
"Usage Note: The first use of harebrained dates to 1548. The spelling hairbrained also has a long history, going back to the 1500s when hair was a variant spelling of hare. The hair variant was preserved in Scotland into the 18th century, and as a result it is impossible to tell exactly when people began writing hairbrained in the belief that the word means "having a hair-sized brain" rather than "with no more sense than a hare." While hairbrained continues to be used and confused, it should be avoided in favor of harebrained which has been established as the correct spelling."
http://dictionary.reference.com/browse/harebrained