1. The 2000th anniversary (or the celebration of it)
   "Rome marked the bimillennium of Augustus's death with special exhibitions";
   - bimillenary
    
2. A span of 2000 years
   "The bimillennium of Rome's founding was celebrated in 1753";
   - bimillenary

Derived forms: bimillenniums

Type of: anniversary, day of remembrance, period, period of time, time period, time span