The Collaborative International Dictionary of English v.0.48:

Neuter \Neu"ter\, a. [L., fr. ne not + uter whether; akin to E.
   whether. See No, and Whether, and cf. Neither.]
   1. Neither the one thing nor the other; on neither side;
      impartial; neutral. [Archaic]
      [1913 Webster]

            In all our undertakings God will be either our
            friend or our enemy; for Providence never stands
            neuter.                               --South.
      [1913 Webster]

   2. (Gram.)
      (a) Having a form belonging more especially to words which
          are not appellations of males or females; expressing
          or designating that which is of neither sex; as, a
          neuter noun; a neuter termination; the neuter gender.
      (b) Intransitive; as, a neuter verb.
          [1913 Webster]

   3. (Biol.) Having no generative organs, or imperfectly
      developed ones; sexless. See Neuter, n., 3.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

neuter \neu"ter\, v. t.
   To render incapable of sexual reproduction; to remove or
   alter the sexual organs so as to make infertile; to alter; to
   fix; to desex; -- in male animals, to castrate; in female
   animals, to spay.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Neuter \Neu"ter\, n.
   1. A person who takes no part in a contest; one who is either
      indifferent to a cause or forbears to interfere; a
      neutral.
      [1913 Webster]

            The world's no neuter; it will wound or save.
                                                  --Young.
      [1913 Webster]

   2. (Gram.)
      (a) A noun of the neuter gender; any one of those words
          which have the terminations usually found in neuter
          words.
      (b) An intransitive verb.
          [1913 Webster]

   3. (Biol.) An organism, either vegetable or animal, which at
      its maturity has no generative organs, or but imperfectly
      developed ones, as a plant without stamens or pistils, as
      the garden Hydrangea; esp., one of the imperfectly
      developed females of certain social insects, as of the ant
      and the common honeybee, which perform the labors of the
      community, and are called workers.
      [1913 Webster]

WordNet (r) 3.0 (2006):

neuter
    adj 1: of grammatical gender; "`it' is the third-person singular
           neuter pronoun" [ant: feminine, masculine]
    2: having no or imperfectly developed or nonfunctional sex
       organs [syn: neuter, sexless]
    n 1: a gender that refers chiefly (but not exclusively) to
         inanimate objects (neither masculine nor feminine)
    v 1: remove the ovaries of; "Is your cat spayed?" [syn: alter,
         neuter, spay, castrate]

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "neuter":
   Laodicean, alter, animate, anythingarian, apathetic, asexual,
   capon, castrate, castrated, centrist, change, cold, common gender,
   contemplative, cool, cut, desex, desexualize, do-nothing, doctor,
   dormant, emasculate, emasculated, epicene, eunuchize, eunuchized,
   even, feminine, fence-sitter, fervorless, fifty-fifty, fix, frigid,
   frustrated, geld, gender, half-and-half, halfhearted, idle,
   immobile, impartial, impotent, inactive, inanimate, independent,
   indifferent, inert, laissez-aller, laissez-faire, lukewarm,
   masculine, meditative, midway, moderate, motionless, mugwump,
   mutilate, neutral, nonaligned, noncommitted, nonpartisan,
   nothingarian, on the fence, paralytic, paralyzed, passive,
   perfunctory, procrastinating, quiescent, quietist, quietistic,
   sexless, spay, stagnant, stagnating, standpat, static, stationary,
   tepid, third force, third world, third-force, third-world,
   uncommitted, uninvolved, unsex, unsexed, unsexual, vegetable,
   vegetative, zealless