The Collaborative International Dictionary of English v.0.48:

R'eseau \R['e]`seau"\ (r[=a]`z[=o]"), n. [F.]
   A network; specif.:
   (a) (Astron.) A system of lines forming small squares of
       standard size, which is photographed, by a separate
       exposure, on the same plate with star images to
       facilitate measurements, detect changes of the film, etc.
   (b) In lace, a ground or foundation of regular meshes, like
       network.
       [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

reseau
    n 1: a net or mesh foundation for lace
    2: a network of fine lines used by astronomers as a reference
       for measurements on star photographs