Every one third of a year.
Semester
we have a semiannual banquet for our club that happens every 6 months
Something that occurs everyday is said to be quotidian. An example of a sentence using the word would be: Her quotidian commute was thankfully shorter now that she got transferred.
The word 'word' occurs in the kjv in 675 times.
Quarterly
Annually.
Quarter. At every Quarter of the financial year (every 3 months).
Biannual describes something that occurs twice a year, once every half year.
Something that is annual occurs once every year. It does not refer to something that occurs continually throughout a year. Something that lasts or continues for a long or apparently indefinite time would be called perennial.
Something that is annual occurs once every year. It does not refer to something that occurs continually throughout a year. Something that lasts or continues for a long or apparently indefinite time would be called perennial.
From the Related Link below: ; bimonthly / semimonthly : Bimonthly is an adjective that means every two months: "I brought the cake for the bimonthly office party." Bimonthlyis also a noun that means a publication issued every two months: "The company publishes several popular bimonthlies." Semimonthly is an adjective that means happening twice a month: "We have semimonthly meetings on the 1st and the 15th."
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.
A ten letter word for something that occurs could be an occurrence or happenings.
vicennial
A synonym for every five years is quinquennial: as an adjective describes something that happens every five years or that lasts for five years; the noun means the fifth anniversary or a period of five years.
Quinquennial = something that happens every 5 years. Lustral = also something that happens every 5 years or we could invent: semi-Decennial: where semi is half and Deccennial happens every 10 years.