we have a semiannual banquet for our club that happens every 6 months
Once every 12 months, once every 6 months, once every 3 months
there are 12 months in every Gregorian year.
Every three months is called a quarter. And there are four quarters in a year.
120 months. 12 for every year.
Quarter. At every Quarter of the financial year (every 3 months).
Moores law states that the number of discrete logical components on an area of silicone will double every eighteen months (his grammer is better). this means that every eighteen months the speed/capasity of a device should roughly double, giveing engineers twice as much process to play with and invent new stuff based on.
Bi-monthly means every two months. (Semi-monthly means twice a month). There may be cases where these terms are misused, so be careful.
According to the online Oxford Dictionaries, "bimonthly" can refer to something occurring every two months or twice in one month. It might be best to just say "every two months" to avoid confusion.
weekly
twice-a-day or it can be called semi-diurnal which relates to such occurrences as tides.
Something that happens once a century.
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Quarterly
A triennial event happens every three years.
Something that happens every 5 years
Annual.