| Answer | Crossword Clue |
|---|---|
| BIENNIAL | Happening once in two years. |
| sexennially | SEXENNIAL, lasting six years, or happening once in six years |
| sexennial | lasting six years, or happening once in six years / a six-year anniversary |
| bimillennial | happening every two thousand years |
| bimillenary | happening every two thousand years / a two thousandth anniversary |
| bicentennial | happening every two hundred years / a two hundred year anniversary also BICENTENARY |
| bicentenary | happening every two hundred years / a two hundred year anniversary also BICENTENNIAL |
