The Collaborative International Dictionary of English v.0.48:

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]

The Collaborative International Dictionary of English v.0.48:

Circular \Cir"cu*lar\, a. [L. circularis, fr. circulus circle:
   cf. F. circulaire. See Circle.]
   [1913 Webster]
   1. In the form of, or bounded by, a circle; round.
      [1913 Webster]

   2. repeating itself; ending in itself; reverting to the point
      of beginning; hence, illogical; inconclusive; as, circular
      reasoning.
      [1913 Webster]

   3. Adhering to a fixed circle of legends; cyclic; hence,
      mean; inferior. See Cyclic poets, under Cyclic.
      [1913 Webster]

            Had Virgil been a circular poet, and closely adhered
            to history, how could the Romans have had Dido?
                                                  --Dennis.
      [1913 Webster]

   4. Addressed to a circle, or to a number of persons having a
      common interest; circulated, or intended for circulation;
      as, a circular letter.
      [1913 Webster]

            A proclamation of Henry III., . . . doubtless
            circular throughout England.          --Hallam.
      [1913 Webster]

   5. Perfect; complete. [Obs.]
      [1913 Webster]

            A man so absolute and circular
            In all those wished-for rarities that may take
            A virgin captive.                     --Massinger.
      [1913 Webster]

   Circular are, any portion of the circumference of a circle.


   Circular cubics (Math.), curves of the third order which
      are imagined to pass through the two circular points at
      infinity.

   Circular functions. (Math.) See under Function.

   Circular instruments, mathematical instruments employed for
      measuring angles, in which the graduation extends round
      the whole circumference of a circle, or 360[deg].

   Circular lines, straight lines pertaining to the circle, as
      sines, tangents, secants, etc.

   Circular note or Circular letter.
      (a) (Com.) See under Credit.
      (b) (Diplomacy) A letter addressed in identical terms to a
          number of persons.

   Circular numbers (Arith.), those whose powers terminate in
      the same digits as the roots themselves; as 5 and 6, whose
      squares are 25 and 36. --Bailey. --Barlow.

   Circular points at infinity (Geom.), two imaginary points
      at infinite distance through which every circle in the
      plane is, in the theory of curves, imagined to pass.

   Circular polarization. (Min.) See under Polarization.

   Circular sailing or Globular sailing (Naut.), the method
      of sailing by the arc of a great circle.

   Circular saw. See under Saw.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Circular \Cir"cu*lar\, n. [Cf. (for sense 1) F. circulaire,
   lettre circulaire. See Circular, a.]
   [1913 Webster]
   1. A circular letter, or paper, usually printed, copies of
      which are addressed or given to various persons; as, a
      business circular.
      [1913 Webster]

   2. A sleeveless cloak, cut in circular form.
      [1913 Webster]

WordNet (r) 3.0 (2006):

circular
    adj 1: having a circular shape [syn: round, circular] [ant:
           square]
    2: describing a circle; moving in a circle; "the circular motion
       of the wheel" [syn: circular, rotary, orbitual]
    n 1: an advertisement (usually printed on a page or in a
         leaflet) intended for wide distribution; "he mailed the
         circular to all subscribers" [syn: circular, handbill,
         bill, broadside, broadsheet, flier, flyer,
         throwaway]

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "circular":
   O-shaped, actuate, ambagious, anfractuous, announcement, annular,
   annulate, annulose, annunciation, backhanded, booklet, brochure,
   bulletin board, chapbook, circinate, circuitous, circulate,
   circumlocutory, comic book, communique, coronary, crownlike,
   cyclic, cycloid, declaration, deviating, deviative, devious,
   diffuse, digressive, discoid, discursive, disklike, disperse,
   disseminate, distribute, edict, encyclical, enunciation, exchange,
   excursive, fallacious, flow, folder, helical, illogical,
   inconsistent, indirect, interchange, irrational, leaflet,
   manifesto, meandering, notice, notification, oblique, orbital,
   out-of-the-way, pamphlet, periphrastic, position paper,
   proclamation, program, programma, pronouncement, pronunciamento,
   propagate, public notice, radiate, redundant, report, revolve,
   ring-shaped, ringlike, rotary, rotate, round, roundabout, rounded,
   set off, sophistic, sophistical, spiral, statement, strew,
   tortuous, tract, twisted, twisting, ukase, white book,
   white paper