[Lazy_Perfectionist]

Technically, we _have_ them, but we don't use them much outside of literature. As an aside, we're not the only ones. The Spanish, Italian, etc... tend to use fifteen-day units.

Fiscally, we use bi-weekly, for some payroll systems. It's the same thing, but nope, I've never seen a fortnight used outside of classical (read, imported from europe, not Upton Sinclair's the Jungle, but Shakespeare's Hamlet) literature.