The Collaborative International Dictionary of English v.0.48:

Portico \Por"ti*co\, n.; pl. Porticoesor Porticos. [It., L.
   porticus. See Porch.] (Arch.)
   A colonnade or covered ambulatory, especially in classical
   styles of architecture; usually, a colonnade at the entrance
   of a building.
   [1913 Webster]