Fortnightly
A fortnight is a unit of time equal to 14 days (2 weeks). The word derives from the Old English: fēowertyne niht, meaning “fourteen nights”.
Some wages and salaries are paid on a fortnightly basis; however in North America it is far more common to use the term biweekly. Neither of these terms should be confused with semimonthly, which divides a year into exactly 24 periods (12 months × 2), instead of the 26 (≈52 weeks ÷ 2) of fortnightly/biweekly.
Biweekly
Biweekly may refer to occurring twice a week, or occurring every two weeks. Due to this ambiguity, many style guides recommend to never use the term and to replace with unambiguous expressions.
There are 52 full weeks in a year of 12 months (ISO 8601 defines a year as containing 52 or 53 weeks), making for a possible 26 or 104 biweekly events in a year. This is a greater number than if such events were held twice a month, because most months have more than four weeks (28 days).
In the United Kingdom, Australia and New Zealand, the term fortnightly is more commonly used for an event that occurs every two weeks. In the US, a biweekly publication is issued every two weeks and a bimonthly publication is issued every two months. New York State SNAP refers to a biweekly paycheck as every 2 weeks.
Fortnightly (noun)
a publication issued fortnightly (once every two weeks); a bi-weekly (one sense)
Fortnightly (adjective)
occurring once in a fortnight; once every two weeks
Fortnightly (adverb)
once in a fortnight; once every two weeks
Biweekly (adjective)
Occurring once every two weeks.
Biweekly (adjective)
Occurring twice a week (but see the Usage notes).
Biweekly (adverb)
Every two weeks.
Biweekly (adverb)
Twice a week (but see the Usage notes).
Biweekly (noun)
Something that is published or released once every two weeks.
“The local paper is a biweekly.”