Cock a Snook

Meaning

A derisive gesture.

Origin

In trying to explain the origin of 'Cock a snook' it would be helpful to know what a snook is. Unfortunately we don't really. There is a species of fish called snook, but it isn't that, unless there's a form of derisive gesture that I've had too sheltered an upbringing to be aware of. A snook is also a promontory of jutting out land. That could have something to do with the gesture as it does involve sticking fingers out. Apart from this single phrase, snook isn't a word you would expect to hear very often. It is sometimes reported to be derived from snout, as in thumbing one's nose. That's possible but, although snout and snook are somewhat similar, why didn't they just 'cock a snout'. That term doesn't appear to be recorded.

The general understanding of what's meant by 'cock a snook' is the spread hand with thumb on the nose, preferably with crossed eyes, waggling fingers and any other annoying gesticulation that comes to mind at the time. It's what the Americans call 'the five-fingered salute'.

The use of cock is also difficult to explain. Again it might refer to the sticking out and turning up of the fingers. That would be in line with the term cocked-hat in which the brim is turned up jauntily. It could also be a reference to the shape of a cock's comb, which is rather like the shape of the gesture. It took some time for the gesture as we now know it to be established - various other forms were used in the past.

The first reference I can find that mentions the phrase is Wynne's Diary, 1791:

"They cock snooks at one on every occasion."

That gives no clue as to what was meant by the term. The next time we see it is in Augustus Hare's The story of my life, 1879:

"If I put my hands so ... (cutting a snooks), they might reproach me very much indeed."

This provides little more clarity. Is 'cutting a snooks' even the same thing? Then, in The Times, 1904, we have "The young monkey puts his tongue in his cheek and cocks a snook at you.", which makes no reference to any sort of hand gesture.

All in all, this is an odd phrase and we know precious little about its origin.
Above quoted with thanks from Phrases.org a site that digs deep into the origin of phrases