Green’s Dictionary of Slang

1. a flighty woman.

1932

‘R. Scully’ Scarlet Pansy 354: The ‘Frenchie’ displayed her wares, opening her mouth wide, revealing her pink tongue, rolling her eyes.

2. (US gay) a fellator.

1930		N. Kimball Amer. Madam (1981) 130: Frenchy was the house specialist for those johns who like extra exotic attentions.
1937		Confessions Eng. Maid 38: There was Heloise, whom everyone called Frenchy, who would suck another girl off for any trifling payment [Simes:DLSS].
1965		K. Marlowe Mr Madam (1967) 149: ‘I think my name is Frenchy ...’ They all laughed.
1972		B. Rodgers Queens’ Vernacular.

3. (US Und.) an act of fellatio, usu. as offered by a prostitute.

1958		Murtagh & Harris Cast the First Stone 205: ‘Do you French?’ I said [...] ‘Four dollars for French. O.K. for four dollars for a Frenchy?’.
1967		in S. Harris Hellhole 91: And she said, ‘Twenty bucks.’ And I said, ‘What do I get for that?’ And she said, ‘A straight or Frenchy if you want it.’.
1977		E. Torres Q&A 169: Okay, but only a quick Frenchie. Give me the hundred.

4. a French kiss.

1996		Irish Times 21 May 🌐 Clearly no 11 or 12 year old child is emotionally ready to deal with the sexual feelings aroused by ‘shifting’, ‘meeting’ or ‘getting off’ the slang terms widely used for ‘a Frenchie’.
2006		D. Mitchell Black Swan Green 249: Give Mummy a Frenchie, die yer?