The Collaborative International Dictionary of English v.0.48:

Regular \Reg"u*lar\ (-l?r), a. [L. regularis, fr. regula a rule,
   fr. regere to guide, to rule: cf. F. r['e]gulier. See
   Rule.]
   [1913 Webster]
   1. Conformed to a rule; agreeable to an established rule,
      law, principle, or type, or to established customary
      forms; normal; symmetrical; as, a regular verse in poetry;
      a regular piece of music; a regular verb; regular practice
      of law or medicine; a regular building.
      [1913 Webster]

   2. Governed by rule or rules; steady or uniform in course,
      practice, or occurence; not subject to unexplained or
      irrational variation; returning at stated intervals;
      steadily pursued; orderlly; methodical; as, the regular
      succession of day and night; regular habits.
      [1913 Webster]

   3. Constituted, selected, or conducted in conformity with
      established usages, rules, or discipline; duly authorized;
      permanently organized; as, a regular meeting; a regular
      physican; a regular nomination; regular troops.
      [1913 Webster]

   4. Belonging to a monastic order or community; as, regular
      clergy, in distinction dfrom the secular clergy.
      [1913 Webster]

   5. Thorough; complete; unmitigated; as, a regular humbug.
      [Colloq.]
      [1913 Webster]

   6. (Bot. & Zool.) Having all the parts of the same kind alike
      in size and shape; as, a regular flower; a regular sea
      urchin.
      [1913 Webster]

   7. (Crystallog.) Same as Isometric.
      [1913 Webster]

   Regular polygon (Geom.), a plane polygon which is both
      equilateral and equiangular.

   Regular polyhedron (Geom.), a polyhedron whose faces are
      equal regular polygons. There are five regular
      polyhedrons, -- the tetrahedron, the hexahedron, or cube,
      the octahedron, the dodecahedron, and the icosahedron.

   Regular sales (Stock Exchange), sales of stock deliverable
      on the day after the transaction.

   Regular troops, troops of a standing or permanent army; --
      opposed to militia.
      [1913 Webster]

   Syn: Normal; orderly; methodical. See Normal.
        [1913 Webster]

WordNet (r) 3.0 (2006):

regular polygon
    n 1: a polygon with all sides and all angles equal