Source : Webster's Revised Unabridged Dictionary (1913)

Curvilineal \Cur`vi*lin"e*al\ (-al), Curvilinear
\Cur`vi*lin"e*ar\ (-?r), a. [L. curvus bent + E. lineal,
   linear.]
   Consisting of, or bounded by, curved lines; as, a curvilinear
   figure.

Source : WordNet®

curvilinear
     adj : characterized by or following a curved line; "curvilinear
           tracery"; "curvilinear motion" [syn: {curvilineal}]