Regarding Facilities and Areas and the Status of United States Armed Forces in Japan, signed at Tokyo on January 25, 2008, Noting situations involving both countries,
Familiarity information: BICENTENNIAL used as a noun is very rare. â¢ BICENTENNIAL (adjective). The adjective BICENTENNIAL has 1 sense: 1. of or relating to or completing a period of 200 years. Familiarity information: BICENTENNIAL used as an adjective is very rare.
Update: dictionary.com says twice a year... it continues with the definition with every two years: Biennial. In Britain, it seems, it might mean both... but in the U.S. biannual means twice a year.