Lewis and Short have a different take on the masculine/feminine division of diēs. They claim that diēs is properly masculine, but appears in poetry (metrī gratiā) as a feminine noun to mean ‘day’ in prose to mean ‘time’ or ‘date.’
They pull a number of examples from Ennius, Ovid, Horace and Vergil to support this, but then also lay bare that Julius Caesar (feminine) and Sallust (masculine) use the two genders of diēs for the same phrases. What are your thoughts on this?
Caesar actually uses a variety of diēs phrases:
postridiē eius diē : after that day
diem ex diē dūcere : to lead (troops) day by day
The phrase in diēs is generally translated ‘every day.’ Cf. cotidiē and in diem, which mean roughly the same.
The feminine uses of diēs in prose are generally of a piece: dictā, edictā, cōnstitūtā, praestitūtā, pacta, statā, annuā… you get the idea.
A few more phrases:
- dicere diem alicuī : to bring a charge against someone (by specifying a court day)
- diēs natālis : birthday
- in diem vīvere : to live day-to-day (paycheck-to-paycheck, so to speak—hopefully few of my readers!)