Source : Webster's Revised Unabridged Dictionary (1913)

Fortnightly \Fort"night`ly\, a.
   Occurring or appearing once in a fortnight; as, a fortnightly
   meeting of a club; a fortnightly magazine, or other
   publication. -- adv. Once in a fortnight; at intervals of a
   fortnight.

Source : WordNet®

fortnightly
     adj : occurring every two weeks [syn: {biweekly}]
     adv : every two weeks; "he visited his cousins fortnightly" [syn:
           {biweekly}]