The Collaborative International Dictionary of English v.0.48:

Pear \Pear\ (p[^a]r), n. [OE. pere, AS. peru, L. pirum: cf. F.
   poire. Cf. Perry.] (Bot.)
   The fleshy pome, or fruit, of a rosaceous tree (Pyrus
   communis), cultivated in many varieties in temperate
   climates; also, the tree which bears this fruit. See Pear
   family, below.
   [1913 Webster]

   Pear blight.
   (a) (Bot.) A name of two distinct diseases of pear trees,
       both causing a destruction of the branches, viz., that
       caused by a minute insect (Xyleborus pyri), and that
       caused by the freezing of the sap in winter. --A. J.
       Downing.
   (b) (Zool.) A very small beetle (Xyleborus pyri) whose
       larv[ae] bore in the twigs of pear trees and cause them
       to wither.

   Pear family (Bot.), a suborder of rosaceous plants
      (Pome[ae]), characterized by the calyx tube becoming
      fleshy in fruit, and, combined with the ovaries, forming a
      pome. It includes the apple, pear, quince, service berry,
      and hawthorn.

   Pear gauge (Physics), a kind of gauge for measuring the
      exhaustion of an air-pump receiver; -- so called because
      consisting in part of a pear-shaped glass vessel.

   Pear shell (Zool.), any marine gastropod shell of the genus
      Pyrula, native of tropical seas; -- so called from the
      shape.

   Pear slug (Zool.), the larva of a sawfly which is very
      injurious to the foliage of the pear tree.
      [1913 Webster]
      [1913 Webster]

WordNet (r) 3.0 (2006):

pear blight
    n 1: a disease blackening the leaves of pear and apple trees
         [syn: fire blight, pear blight]