A guide for dummies like me who flunked bonehead english in college.
Don't send me mail about my spelling :-). I actually fixed spelling errors I found in wikipedia, but have introduced my own. The spell checker in my web authoring software isn't perfect either.

Time/Date Anniversaries, repeating events:

biennial - Occurring every two years.
biannual - Occurring twice a year.
semiannual - half-yearly
Quinquennial - 5 years
Decennial - 10 years
Semicentennial, Semi-centennial- 50 years
Centennial - 100 years
Sesquicentennial - 150 years
Bicentennial - 200 years

first week of the year - That week which includes the first Thursday of the year.
his way the first week of the year does not start with a long weekend (Friday to Sunday),
as the New Year's Day itself is a holiday in many countries.

"next week" said on Sunday means "the week beginning tomorrow".
first day of the week:
   USA - Monday
   Most of Europe - Sunday