Source : Webster's Revised Unabridged Dictionary (1913)

Equilateral \E`qui*lat"er*al\, a. [L. aequilateralis; aequus
   equal + latus, lateris, side: cf. F. ['e]quilat['e]ral.]
   Having all the sides equal; as, an equilateral triangle; an
   equilateral polygon.

   {Equilateral hyperbola} (Geom.), one whose axes are equal.

   {Equilateral shell} (Zo["o]l.), one in which a transverse
      line drawn through the apex of the umbo bisects the valve,
      or divides it into two equal and symmetrical parts.

   {Mutually equilateral}, applied to two figures, when every
      side of the one has its equal among the sides of the
      other.