triennial
    adj 1: occurring every third year or lasting 3 years
    n 1: the 300th anniversary (or the celebration of it) [syn:
         tercentennial, tercentenary, triennial]

Triennial \Tri*en"ni*al\, n.
   Something which takes place or appears once in three years.
   [1913 Webster]

Triennial \Tri*en"ni*al\, a. [L. triennium the space of three
   years; tri- (see Tri-) + annus year. See Annual.]
   1. Continuing three years; as, triennial parliaments; a
      triennial reign. --Howell.
      [1913 Webster]

   2. Happening, coming about, or appearing once in every three
      years; as, triennial elections; a triennial catalogue; a
      triennial visitation. --T. Warton.
      [1913 Webster]

Cyclic \Cyc"lic\ (s?k"l?k or s?"kl?k), Cyclical \Cyc"lic*al\
   (s?k"l?-kal), a. [Cf. F. cycluque, Gr. kykliko`s, fr. ky`klos
   See Cycle.]
   1. Of or pertaining to a cycle or circle; moving in cycles;
      as, cyclical time. --Coleridge.
      [1913 Webster]

   2. (Chemistry) Having atoms bonded to form a ring structure.
      Opposite of acyclic.

   Note: Used most commonly in respect to organic compounds.

   Note: [Narrower terms: bicyclic; heterocyclic;
         homocyclic, isocyclic]

   Syn: closed-chain, closed-ring.
        [WordNet 1.5]

   3. Recurring in cycles[2]; having a pattern that repeats at
      approximately equal intervals; periodic. Opposite of
      noncyclic.

   Note: [Narrower terms: alternate(prenominal),
         alternating(prenominal); alternate(prenominal), every
         other(prenominal), every second(prenominal);
         alternating(prenominal), oscillating(prenominal);
         biyearly; circadian exhibiting 24-hour
         periodicity); circular; daily, diurnal;
         fortnightly, biweekly; hourly; midweek,
         midweekly; seasonal; semestral, semestrial;
         semiannual, biannual, biyearly; semiweekly,
         biweekly; weekly; annual, yearly; biennial;
         bimonthly, bimestrial; half-hourly; half-yearly;
         monthly; tertian, alternate(prenominal);
         triennial]
         [WordNet 1.5]

   4. Marked by repeated cycles[2].
      [WordNet 1.5]

   Cyclic chorus, the chorus which performed the songs and
      dances of the dithyrambic odes at Athens, dancing round
      the altar of Bacchus in a circle.

   Cyclic poets, certain epic poets who followed Homer, and
      wrote merely on the Trojan war and its heroes; -- so
      called because keeping within the circle of a single
      subject. Also, any series or coterie of poets writing on
      one subject. --Milman.
      [1913 Webster]