Definition of "tetched"

"His mind was as keen as a razor, an' as straight-edged, 'xcept jest on one subject. On that he was, so to say, a little—wal—a little tetched."

1889, Laura E. Richards, chapter 9, in Queen Hildegarde

Just because he has trouble with the last verse of the Star Spangled Banner doesn't mean he's tetched. Maybe he has a mental block because you've been hammering him over the skull for three years about it.

1959 April 21, Ann Landers, "Oh Why Can't He See 'Dawn's Early Light'?, St. Petersburg Times (USA) (retrieved 26 June 2012)

There's a murderer about, but how can you spot him when everyone is moon-tetched?

1982 Sep. 27, Mary Cantwell, "Books Of The Times" (review of Goosefoot by Patrick McGinley), New York Times (retrieved 26 June 2012)

"They ain't bin tetched or handled by any one but the Kempany's agents."

1899, Bret Harte, “Dick Spindler's Family Christmas”, in Mr. Jack Hamlin's Mediation and Other Stories

"That bullet never tetched ye!"

c. 1900, O. Henry, The Reformation Of Calliope