The Collaborative International Dictionary of English v.0.48:
bimillennium \bimillennium\ n. 1. a span of 2000 years. Syn: bimillenary. [WordNet 1.5] 2. the year 2000 a. d. [PJC]WordNet (r) 3.0 (2006):
bimillennium n 1: the 2000th anniversary (or the celebration of it) [syn: bimillennium, bimillenary] 2: a span of 2000 years [syn: bimillennium, bimillenary]