Source : Webster's Revised Unabridged Dictionary (1913)

Patera \Pat"e*ra\, n.; pl. {Pater[ae]}(?). [ L., fr. patere to
   lie open.]
   1. A saucerlike vessel of earthenware or metal, used by the
      Greeks and Romans in libations and sacrificies.

   2. (Arch.) A circular ornament, resembling a dish, often
      worked in relief on friezes, and the like.