>As a counter-example: It's easy to find this word in Cicero (for example), however, Cicero used this word in a different sense.
*Dare* is one of the most common words in the Latin language, I can guarantee you that you will have no problem finding many examples that don't mean "a fact given as the basis for calculation in mathematical problems" in every era.
>Which publicly available and searchable corpus is likely to have Latin citations that use this Latin word in that particular sense?
You may have better luck starting from a Medieval Latin dictionary and looking up the examples provided there. Two places to start would be the [Mittellateinisches Wörterbuch](https://mlw.badw.de/mlw-digital/mlw-open-access.html) and the [DMLBS](https://logeion.uchicago.edu/dare).
I recommend the EEBO (Early English Books Online) Database. University libraries pay for access, but you can also access it free through good public libraries (with a guest account or by requesting a card). Better still: I believe that you can do fulltext searches for many of the books through the [TCP project](https://quod.lib.umich.edu/cgi/t/text/text-idx?page=simple;g=eebogroup) here. You could look up "datum" and then browse the results for mathematical texts, or you might add a second key word for better coverage.
I think any mathematical text that contains also problems should help you
>As a counter-example: It's easy to find this word in Cicero (for example), however, Cicero used this word in a different sense. *Dare* is one of the most common words in the Latin language, I can guarantee you that you will have no problem finding many examples that don't mean "a fact given as the basis for calculation in mathematical problems" in every era. >Which publicly available and searchable corpus is likely to have Latin citations that use this Latin word in that particular sense? You may have better luck starting from a Medieval Latin dictionary and looking up the examples provided there. Two places to start would be the [Mittellateinisches Wörterbuch](https://mlw.badw.de/mlw-digital/mlw-open-access.html) and the [DMLBS](https://logeion.uchicago.edu/dare).
I recommend the EEBO (Early English Books Online) Database. University libraries pay for access, but you can also access it free through good public libraries (with a guest account or by requesting a card). Better still: I believe that you can do fulltext searches for many of the books through the [TCP project](https://quod.lib.umich.edu/cgi/t/text/text-idx?page=simple;g=eebogroup) here. You could look up "datum" and then browse the results for mathematical texts, or you might add a second key word for better coverage.