Webster's Revised Unabridged Dictionary · 1913

Letch

Letch (lech) , verb and noun

See Leach.

Letch , noun

[See Lech, Lecher.]

1.
Strong desire; passion; especially, lust. [Archaic]
Some people have a letch for unmasking impostors, or for avenging the wrongs of others. — De Quincey
2.
A lecher. [slang]