The same Latin verb dare, to give, gave us both the word ‘date’ and ‘data’. It must be the language’s most generous word. And we cannot avoid this inheritance, as our culture is based on the mastery of time and on the data and facts informing and guiding many of our private decisions and public policies.
Etymologically speaking, the data predates the date. The neuter singular past participle of the Latin dare, to give, is datum, given, modified for neuter plural as data, the things that have been given. The words datum and data had an existence in classical and medieval Latin for facts used in mathematical calculations.
The date, on the other hand, harks back to a different use of the Latin data. Dating letters makes more sense than dating emails or other instant communication methods, because of the gap between the time the letter has been written and the time it is received. Before the age of mass and electric communication, letters could take weeks and sometimes months to be delivered, so knowing exactly when the letter had been written was key. Dating letters in classical and medieval times was done by adding what’s called a ‘dating clause’ at the very end of the letter. The letter was written or ‘given’ (data) by the sender to the receiver. The dating clause usually began with the word ‘data’ followed by the place and calendar date. The 1215 issue of Magna Carta, although not necessarily a letter, followed the same convention. It ended, fairly typically, with a date clause:
Data per manum nostram in prato quod vocatur Ronimed inter Windlesoram et Stanes, quinto dccimo die Junii, anno regni nostri decimo septimo.
Given by our hand in the meadow which is called Runnymede, between Windsor and Staines, on the fifteenth day of June, in the seventeenth year of our reign (1215).
The data clause (feminine of datum because the document, whether letter (littera, epistola), charter (carta), etc, was a femine noun) was so common that vernacular languages picked it up metonymically as it was, the data becoming the date. What’s today’s date really means ‘what’s the data clause of today’s letter’?