Source : Webster's Revised Unabridged Dictionary (1913)

Unicursal \U`ni*cur"sal\, a. [Uni- + L. currere, cursum, to
   run.] (Geom.)
   That can be passed over in a single course; -- said of a
   curve when the co["o]rdinates of the point on the curve can
   be expressed as rational algebraic functions of a single
   parameter [theta].

   Note: As [theta] varies minus infinity to plus infinity, to
         each value of [theta] there corresponds one, and only
         one, point of the curve, while to each point on the
         curve there corresponds one, and only one, value of
         [theta]. Straight lines, conic sections, curves of the
         third order with a nodal point, curves of the fourth
         order with three double points, etc., are unicursal.