dementation

From dement +‎ -ation?

dementation (uncountable)

1. (archaic) The act of depriving of reason; madness.
   • 1654, Richard Whitlock, Zootomia; Or, Observations on the Present Manners of the English:

     […] and so they aver to be drunk, or accessory to anothers Distemper (especially supposing the Distemper under command from breaking out into any other sins besides its own dementation, or stupidity) to be a lesse sin, than to call one Drunkard, on the bare sight of him in a Distemper, or but one slender Information.

• “dementation”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.