Playing with words: Biannual vs Biennial

So these are two words that I often seem people use interchangeably. They both have something to do with 'two' and 'yearly', but let me say it right from the start - they do not mean the same thing.

BIANNUAL
[bahy-an-yoo-uh l]

Adjective
1. occurring twice a year; semiannual.

BIENNIAL
[bahy-en-ee-uh l]
Adjective
1. happening every two years:
biennial games.
2. lasting or enduring for two years:
a biennial life cycle.
3. (Botany). completing its normal term of life in two years, flowering and fruiting the second year, as beets or winter wheat.
Noun
4. any event occurring once in two years.
5. (Botany). a biennial plant.
Now you know
Empi