I. adjective
Etymology: fortnight + -ly (adjective suffix)
: occurring, appearing, or being made, done, or acted upon once in two weeks or every two weeks
fortnightly meeting
fortnightly letters
fortnightly tasks
II. adverb
Etymology: fortnight + -ly (adverb suffix)
: once in a fortnight : every fortnight
III. noun
( -es )
Etymology: fortnightly (I)
: a publication issued fortnightly