The Collaborative International Dictionary of English v.0.48:

Campagnol \Cam`pa`gnol"\, n. [F., fr. campagne field.] (Zool.)
   A mouse (Arvicala agrestis), called also meadow mouse,
   which often does great damage in fields and gardens, by
   feeding on roots and seeds.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

fieldmouse \fieldmouse\, field mouse \field mouse\n.
   1. (Zool.) any nocturnal Old World mouse of the genus
      Apodemus inhabing woods and fields and gardens.
      [WordNet 1.5]

   2. (Zool.) any mouse inhabiting fields, as the campagnol
      and the deer mouse. See Campagnol, and Deer mouse.
      [1913 Webster]