Singular or plural for enumerations?

Do you use singular or plural for enumerations? I think it makes best sense with plural in the declaration

enum Weekdays
{
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday,
    Sunday
}

... but I think it makes more sense with singular when using the type, e.g.

Weekday firstDayOfWeek = Weekday.Monday;

I read a recommendation somewhere to use singular whith regular enums and plural with flags, but I would like to hear some more pros and cons.