National Dictionary Day (16 October)

"National" here is American. And the day is the birthday of Noah Webster (16/10/1758-28/5/1843). Author of the "National Dictionary".
Actually called The American Dictionary of the English Language.
Published 1828. 25 years in the making, 2,000 pages, 70,000 entries.
Price $20.00.
"A great number of words in our language require to be defined in a phraseology accommodated to the condition and institutions of the people in these states, and the people of England must look to an American Dictionary for a correct understanding of such terms."
(from the Preface)
This almost reads like a claim that the American senses are the correct ones. But I think he is taking the much more reasonable position that where UK and US usage diverge, if UK speakers want to know about the US usage, it makes sense for them to consult an American dictionary.
Webster's first big success was a Spelling Book (1783), which sold and sold for decades, and made him a household (or schoolroom) name. He had some good ideas about improved spelling, several of which have become standard for USEng.
https://en.wikipedia.org/wiki/Noah_Webster
https://en.wikipedia.org/wiki/Webster%27s_Dictionary