Here is a list of words used to indicate time periods and time intervals.

### Time periods

Bicentennial: A period of 200 years

Biennial: A period of 2 years

Century: A period of 100 years

Decade: A period of 10 years

Centennial: Every 100 years

Decennial: Every 10 years

Leap year: A period of 366 days

Millennium: A period of 1,000 years

Month: A period of 28-31 days

Olympiad: Every 4 years

Quadrennial: Every 4 years

Quadricentennial: Every 400 years

Quincentennial: Every 500 years

Septennial: Every 7 years

Sexcentenary: A period of 600 years

Sexennial: Every 6 years

Tercentenary: A period of 300 years

Triennial: Every 3 years

Vicennial: Every 20 years

Week: 7 days

Year: 365 days

### Time intervals

Annual: occurring every year

Biannual: occurring twice a year

Bimonthly: occurring every two months or twice a month

Biweekly: every two weeks or twice a week

Diurnal: daily, of each day

Perennial: lasting through a year or several years

Semi-annual: occurring twice a year

Semi-diurnal: twice a day

Semi-weekly: twice a week

Trimonthly: every three months

Triweekly: every three weeks or three times a week

Thrice weekly: three times a week