The Collaborative International Dictionary of English v.0.48:

Geometrid \Ge*om"e*trid\, a. (Zool.)
   Pertaining or belonging to the Geometrid[ae].
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Geometrid \Ge*om"e*trid\, n. (Zool.)
   One of numerous genera and species of moths, of the family
   Geometrid[ae]; -- so called because their larv[ae] (called
   loopers, measuring worms, spanworms, and inchworms) creep in
   a looping manner, as if measuring. Many of the species are
   injurious to agriculture, as the cankerworms.
   [1913 Webster]

WordNet (r) 3.0 (2006):

geometrid
    n 1: slender-bodied broad-winged moth whose larvae are called
         measuring worms [syn: geometrid, geometrid moth]