The Collaborative International Dictionary of English v.0.48:

Pyrus \Py"rus\, n. [L. pyrus, or better pirus, pear tree.]
   (Bot.)
   A genus of rosaceous trees and shrubs having pomes for fruit.
   It includes the apple, crab apple, pear, chokeberry, sorb,
   and mountain ash.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Pyrus
    n 1: fruit trees native to the Old World: pears [syn: Pyrus,
         genus Pyrus]