Green’s Dictionary of Slang

letch v.

to lust, crave; thus leching, letching n.

1911		J. Masefield Everlasting Mercy 68: He’s ate the fat and sweet [...] And drunk and leched from day till morrow.
1936		(con. 1920s) Dos Passos Big Money in USA (1966) 884: Actresses leching for stardom made sheepseyes at him.
1965		T. Wolfe Kandy-Kolored Tangerine-Flake Streamline Baby (1966) 78: The inchoate leching you are liable to be doing, what with the bouffant nymphets.
1969		Punch 15 Oct. 639: A set of middle-aged married men leching after sexy secretaries half their age.
1977		E. Torres Q&A 75: He has the morals of a tomcat, his office being conveniently located on the ninth floor, opposite the secretarial pool, where he can letch ad nauseam.
1996		(con. 1964-65) B. Thorpe Sex and Thugs and Rock ’n’ Roll 11: I was still mapping her geography and she caught me letching.
2004		J. Ellroy ‘Hollywood Fuck Pad’ in Destination: Morgue! (2004) 219: I whipped out the Donna shots [...] Russ looked, lingered, leched.
2023		(con. 1962) J. Ellroy Enchanters 159: ‘You leched on her’.

In compounds

letching-piece (n.) [piece n. (1a)]

a promiscuous woman.

1966		Trimble 5000 Adult Sex Words and Phrases.
1984		Partridge DSUE (8th edn) 678: C.20.

In phrases

letch about (v.) (also lech about)

to act in a sexual manner.

1966

T. Keyes All Night Stand 143: Then I have to lech about with all his friends.