According to Aubrey, the author was thought to be crackbrained, and lost much of his practice in consequence.
She had no right to use such a power for the propaganda of crackbrained theories!
People at court laughed at Teynagel and his mission, and Henry treated him as a crackbrained adventurer.
They were of a very various kind, and no bad epitome of the mind of a gallant and crackbrained coxcomb.
Nobody disputed it; or, if any one did, he was set down by the oracles of the vicinage as a crackbrained visionary.
This p. 83came from a hundred children collected by a crackbrained stranger (said to be English).
This woman was a crackbrained devotee, who spent half her time in going to mass and the other half in backbiting her neighbors.
Crazy; eccentric; wild; crackpot (1634+)