Grammatically speaking, I'm not sure if the word French, as used within English, is a modifier, qualifier, or both. Either way, it often also serves as an erotic intensifier, as illustrated by the term French kiss, for example ...
A kiss, as lovers of Casablanca will know, is just a kiss.
But a French kiss, of course, is something else entirely. And whilst some may protest that sticking your tongue into a young woman's mouth isn't the same as sticking your tongue into the holiest of holies, a French kiss is nevertheless in the same ballpark; i.e., it's an act of oral sex, albeit one that doesn't involve direct genital stimulation.
That's why Freud was right to identify amorous kissing as a form of perversion; one that is practiced by even those who would regard themselves as normal, healthy individuals. Put simply, there's nothing natural about oral erotogenic activity in which the the lips, tongue and teeth are diverted from their usual function and turned into secondary sex organs.
And although it may be pleasurable to exchange saliva and play tonsil tennis with a loved one, there's a good reason why the English term this French kissing and that's because they're secretly aware of just how queer it is to use your mouth in such an abberant fashion.
Note: it's ironic that, until recently, the French didn't have a specific term for un baiser amoureux; they described it (rather unromantically) as un baiser avec la langue. It was only in 2014 that the slang term se galocher was accorded official dictionary status.
