From 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]
From WordNet (r) 3.0 (2006) :
Pyrus
n 1: fruit trees native to the Old World: pears [syn: Pyrus,
genus Pyrus]