[Westbrook]

You are absolutely correct.

It is the same in Portuguese.

In Italian, we have ‘la mano’, but for day, ‘il giorno’, so the ending agrees with the gender in the Italian for ‘day’.

Long story short, the protesters are linguistic morons.

[raccoonradio]

Again it may have said un but I typed Una. Forgive me, I speak ingles...

[Verginius Rufus]

Yes, the Spanish word is masculine, but the Latin dies can be either masculine or feminine in the singular (always masculine in the plural).

Italian giorno and French jour come from the Latin adjective diurnus, -a, -um, which is derived from dies.