Rule for masculine · der
Days, months, and seasons are always der.
In German, an entire category of time-related words is always masculine - the days of the week, the months of the year, and the seasons. That's why we say der Freitag, der Sonntag, and der Samstag: every day of the week follows this pattern, just like the months and seasons. This is a semantic rule (based on meaning, not spelling) that covers 26 frequent words in the course, with no exception found. It's one of the safest rules to remember: any day, month, or season takes der.