Cocking a snook

"...[the Oxford Union's] support for Amercia was just a way of cocking
a snook at the French." (New York Times, 2/28/3)
How do you get from "cocking" and "snook" to "thumbing your nose"?

As this one's mostly British, I've deferred to our friends on Greenwich time, but they haven't kprovided an explanation. Webster's Second Unabr. defines "snook" as the nose-thumbing gesture, origin uncertain. Cocking one would be aiming it at somebody.

I thought I'd posted a reply to this one but can't see it. Cocking a snook describes a very old British insult by gesture.

To deal with it the wrong way round, the suspicion is that "snook" is a corruption of "snoot" which itself is a British regional variation on "snout". All makes sense so far...

As for "cocking", if you think about how the gesture is made - placing the thumb on the tip of one's noise, with fingers splayed pointing upwards and then waggled - I'm pretty certain that the "cocking" part comes from coxcomb (or cock's comb if you'd rather), because visually it is a little reminiscent of a rooster's comb. A coxcomb was also an old word for jester or fool, so-called again because of the shape of his cap and bells.

Hence cocking a snook - originally showing someone you think they're a fool, and from there, just being defiant and impertinent.