The Collaborative International Dictionary of English v.0.48:

Mouse \Mouse\ (mous), n.; pl. Mice (m[imac]s). [OE. mous, mus,
   AS. m[=u]s, pl. m[=y]s; akin to D. muis, G. maus, OHG. &
   Icel. m[=u]s, Dan. muus, Sw. mus, Russ. muishe, L. mus, Gr.
   my^s, Skr. m[=u]sh mouse, mush to steal. [root]277. Cf.
   Muscle, Musk.]
   1. (Zool.) Any one of numerous species of small rodents
      belonging to the genus Mus and various related genera of
      the family Muridae. The common house mouse (Mus
      musculus) is found in nearly all countries. The American
      white-footed mouse, or deer mouse (Peromyscus
      leucopus, formerly Hesperomys leucopus) sometimes lives
      in houses. See Dormouse, Meadow mouse, under Meadow,
      and Harvest mouse, under Harvest.
      [1913 Webster]

   2. (Naut.)
      (a) A knob made on a rope with spun yarn or parceling to
          prevent a running eye from slipping.
      (b) Same as 2d Mousing, 2.
          [1913 Webster]

   3. A familiar term of endearment. --Shak.
      [1913 Webster]

   4. A dark-colored swelling caused by a blow. [Slang]
      [1913 Webster]

   5. A match used in firing guns or blasting.
      [1913 Webster]

   Field mouse, Flying mouse, etc. See under Field,
      Flying, etc.

   Mouse bird (Zool.), a coly.

   Mouse deer (Zool.), a chevrotain, as the kanchil.

   Mouse galago (Zool.), a very small West American galago
      (Galago murinus). In color and size it resembles a
      mouse. It has a bushy tail like that of a squirrel.

   Mouse hawk. (Zool.)
      (a) A hawk that devours mice.
      (b) The hawk owl; -- called also mouse owl.

   Mouse lemur (Zool.), any one of several species of very
      small lemurs of the genus Chirogaleus, found in
      Madagascar.

   Mouse piece (Cookery), the piece of beef cut from the part
      next below the round or from the lower part of the latter;
      -- called also mouse buttock.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Deer \Deer\ (d[=e]r), n. sing. & pl. [OE. der, deor, animal,
   wild animal, AS. de['o]r; akin to D. dier, OFries. diar, G.
   thier, tier, Icel. d[=y]r, Dan. dyr, Sw. djur, Goth. dius; of
   unknown origin. [root]71.]
   1. Any animal; especially, a wild animal. [Obs.] --Chaucer.
      [1913 Webster]

            Mice and rats, and such small deer.   --Shak.
      [1913 Webster]

            The camel, that great deer.           --Lindisfarne
                                                  MS.
      [1913 Webster]

   2. (Zool.) A ruminant of the genus Cervus, of many species,
      and of related genera of the family Cervid[ae]. The
      males, and in some species the females, have solid
      antlers, often much branched, which are shed annually.
      Their flesh, for which they are hunted, is called
      venison.
      [1913 Webster]

   Note: The deer hunted in England is Cervus elaphus, called
         also stag or red deer; the fallow deer is Cervus
         dama; the common American deer is Cervus
         Virginianus; the blacktailed deer of Western North
         America is Cervus Columbianus; and the mule deer of
         the same region is Cervus macrotis. See Axis,
         Fallow deer, Mule deer, Reindeer.
         [1913 Webster]

   Note: Deer is much used adjectively, or as the first part of
         a compound; as, deerkiller, deerslayer, deerslaying,
         deer hunting, deer stealing, deerlike, etc.
         [1913 Webster]

   Deer mouse (Zool.), the white-footed mouse (Peromyscus
      leucopus, formerly Hesperomys leucopus) of America.

   Small deer, petty game, not worth pursuing; -- used
      metaphorically. (See citation from Shakespeare under the
      first definition, above.) "Minor critics . . . can find
      leisure for the chase of such small deer." --G. P. Marsh.
      [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]

WordNet (r) 3.0 (2006):

deer mouse
    n 1: brownish New World mouse; most widely distributed member of
         the genus [syn: deer mouse, Peromyscus maniculatus]