Green’s Dictionary of Slang

to kiss with the tongue; thus French kissing n.

1930		(con. 1900s–10s) Dos Passos 42nd Parallel in USA (1966) 314: She taught him how to frenchkiss.
1945		D. Vining A Gay Diary (1996) 19 July 486: He likes French kissing.
1949		‘Swasarnt Nerf’ et al. Gay Girl’s Guide 35: ‘French-kissing’ or ‘soul-kissing’ plays a very deep part in all but the most fleeting affairs.
1949–51		in M. Daly Profile of Youth 68: She had ‘French kissed’ her boyfriend.
1960		G. Swarthout Where the Boys Are 112: The only thing suspect about his innocence was his tendency to French-kiss given the slightest opportunity.
1970		E. Thompson Garden of Sand (1981) 499: Don’t you French kiss?
1988		P. Califia Macho Sluts 29: I love french kissing.
1989		M. Amis London Fields 213: He bit Phoenix on the tongue. Quite far back. Hope she wasn’t letting him French-kiss her again.
1996		(ref. to 1963) D. Healy Bend for Home 176: She drove me home at 4 in the morning and taught me to French-kiss in Main Street.
1998		I. Welsh Filth 346: He pulls Estelle to him and kisses her, pushing his tongue into her mouth [...] French kissin, Ghostie explains.
2000		Guardian Guide 5–11 Feb. 77: Where ‘plural marriage is the norm’ [...] You don’t french kiss your husband in front of another wife.
2002		D.H. Sterry Chicken (2003) 129: The Dixie Chickens fighting and French-kissing.