Nouns

(n)biweeklya periodical that is published twice a week or every two weeks (either 104 or 26 issues per year)

Adjectives

(s)fortnightly, biweeklyoccurring every two weeks
(s)semiweekly, biweeklyoccurring twice a week

Adverbs

(r)semiweekly, biweeklytwice a week“he called home semiweekly”
(r)fortnightly, biweeklyevery two weeks“he visited his cousins fortnightly”