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A massive dictionary of Latin. As of December 2019, the project includes A-M, O-P. It is expected to be completed by 2050.
This is not a Latin-English translation dictionary, but more akin to what the Oxford English Dictionary is for English.
It is being provided open access (free) in large PDF chunks on this website.
A New York Times article describes it thus:
Most dictionaries focus on the most prominent or recent meaning of a word; this one aims to show every single way anyone ever used it, from the earliest Latin inscriptions in the sixth century B.C. to around A.D. 600. The dictionary’s founder, Eduard Wölfflin, who died in 1908, described entries in the T.L.L. not as definitions, but “biographies” of words.
The first entry, for the letter A, was published in 1900. The T.L.L. is expected to reach its final word — “zythum,” an Egyptian beer — by 2050. A scholarly project of painstaking exactness and glacial speed, it has so far produced 18 volumes of huge pages with tiny text, the collective work of nearly 400 scholars, many of them long since dead. The letters Q and N were set aside, because they begin too many difficult words, so researchers will have to go back and work on those, too.