The Collaborative International Dictionary of English v.0.48:

Slander \Slan"der\, v. t. [imp. & p. p. Slandered; p. pr. &
   vb. n. Slandering.]
   1. To defame; to injure by maliciously uttering a false
      report; to tarnish or impair the reputation of by false
      tales maliciously told or propagated; to calumniate.
      [1913 Webster]

            O, do not slander him, for he is kind. --Shak.
      [1913 Webster]

   2. To bring discredit or shame upon by one's acts.
      [1913 Webster]

            Tax not so bad a voice
            To slander music any more than once.  --Shak.
      [1913 Webster]

   Syn: To asperse; defame; calumniate; vilify; malign; belie;
        scandalize; reproach. See Asperse.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Slander \Slan"der\, n. [OE. sclandere, OF. esclandre, esclandle,
   escandre, F. esclandre, fr. L. scandalum, Gr. ??? a snare,
   stumbling block, offense, scandal; probably originally, the
   spring of a trap, and akin to Skr. skand to spring, leap. See
   Scan, and cf. Scandal.]
   1. A false tale or report maliciously uttered, tending to
      injure the reputation of another; the malicious utterance
      of defamatory reports; the dissemination of malicious
      tales or suggestions to the injury of another.
      [1913 Webster]

            Whether we speak evil of a man to his face or behind
            his back; the former way, indeed, seems to be the
            most generous, but yet is a great fault, and that
            which we call "reviling;" the latter is more mean
            and base, and that which we properly call "slander",
            or "Backbiting."                      --Tillotson.
      [1913 Webster]

            [We] make the careful magistrate
            The mark of slander.                  --B. Jonson.
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   2. Disgrace; reproach; dishonor; opprobrium.
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            Thou slander of thy mother's heavy womb. --Shak.
      [1913 Webster]

   3. (Law) Formerly, defamation generally, whether oral or
      written; in modern usage, defamation by words spoken;
      utterance of false, malicious, and defamatory words,
      tending to the damage and derogation of another; calumny.
      See the Note under Defamation. --Burril.
      [1913 Webster]

WordNet (r) 3.0 (2006):

slander
    n 1: words falsely spoken that damage the reputation of another
    2: an abusive attack on a person's character or good name [syn:
       aspersion, calumny, slander, defamation,
       denigration]
    v 1: charge falsely or with malicious intent; attack the good
         name and reputation of someone; "The journalists have
         defamed me!" "The article in the paper sullied my
         reputation" [syn: defame, slander, smirch, asperse,
         denigrate, calumniate, smear, sully, besmirch]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "slander":
   asperse, assail, attack, backbite, backbiting, backstabbing,
   barefaced lie, belie, belittlement, bitchiness, blackwash,
   calumniate, calumniation, calumny, cattiness,
   character assassination, consummate lie, damage, decry, defamation,
   defamation of character, defame, denigrate, depreciation, dirt,
   disparage, disparagement, gossip column, hurt, injure,
   juicy morsel, libel, malicious gossip, malign, misrepresentation,
   monstrous lie, muckrake, muckraking, obloquy, out-and-out lie,
   roorback, scandal, scandalmongering, slur, smear, strumpet, tale,
   tear down, the big lie, tidbit, traduce, traducement, vilification,
   vilify, whispering campaign, whopper



Bouvier's Law Dictionary, Revised 6th Ed (1856):

SLANDER, torts. The defaming a man in his reputation by speaking or writing
words which affect his life, office, or trade, or which tend to his loss of
preferment in marriage or service, or in his inheritance, or which occasion
any other particular damage. Law of Nisi Prius, 3. In England, if slander be
spoken of a peer, or other great man, it is called Scandalum Magnatum.
Falsity and malice are ingredients of slander. Bac. Abr. Slander. Written or
printed slanders are libels; see that word.
     2. Here it is proposed to treat of verbal slander only, which may be
considered with reference to, 1st. The nature of the accusation. 2d. The
falsity of the charge. 3d. The mode of publication. 4th. The occasion; and
5th. The malice or motive of the slander.
     3.-Sec. 1. Actionable words are of two descriptions; first, those
actionable in themselves, without proof of special damages and, secondly,
those actionable only in respect of some actual consequential damages.
     4.-1. Words of the first description must impute: 1st. The guilt of
some offence for which the party, if guilty, might be indicted and punished
by the criminal courts; as to call a person a "traitor," "thief,"
"highwayman;" or to say that he is guilty of "perjury," "forgery," "murder,"
and the like. And although the imputation of guilt be general, without
stating the particulars of the pretended crime, it is actionable. Cro. Jac.
114, 142; 6 T. R. 674; 3 Wils. 186; 2 Vent. 266; 2 New Rep. 335. See 3 Serg.
& Rawle, 255 7 Serg. & Rawle, 451; 1 Binn. 452; 5 Binn. 218; 3 Serg. &
Rawle, 261; 2 Binn. 34; 4 Yeates, 423; 10 Serg. & Rawle, 44; Stark. on
Slander, 13 to 42; 8 Mass. 248; 13 Johns. 124; Id. 275.
     5.-2d. That the party has a disease or distemper which renders him
unfit for society. Bac. Abr. Slander, B 2. An action can therefore be
sustained for calling a man a leper. Cro. Jac. 144 Stark. on Slander, 97.
But charging another with having had a contagious disease is not actionable,
as he will not, on that account, be excluded from society. 2 T. R. 473, 4; 2
Str. 1189; Bac. Abr. tit. Slander, B 2. A charge which renders a man
ridiculous, and impairs the enjoyment of general society, and injures those
imperfect rights of friendly intercourse and mutual benevolence which man
has with respect to man, is also actionable. Holt on Libels, 221.
     6.-3d. Unfitness in an officer, who holds an office to which profit or
emolument is attached, either in respect of morals or inability to discharge
the duties of the office in such a case an action lies. 1 Salk. 695, 698;
Rolle, Ab. 65; 2 Esp. R. 500; 5 Co. 125; 4 Co. 16 a; 1 Str. 617; 2 Ld. Raym.
1369; Bull. N. P. 4; Holt on Libels, 207; Stark. on Slander, 100.
     7.-4th. The want of integrity or capacity, whether mental or pecuniary,
in the conduct of a profession, trade or business, in which the party is
engaged, is actionable, 1 Mal. Entr. 244 as to accuse an attorney or artist
of inability, inattention, or want of integrity; 3 Wils. 187; 2 Bl. Rep.
750; or a clergyman of being a drunkard; 1 Binn. 178; is actionable. See
Holt on Libels, 210; Id. 217.
     8.-2. Of the second class are words which are actionable only in
respect of special damages sustained by the party slandered. Though the law
will not permit in these cases the inference of damage, yet when the damage
has actually been sustained, the party aggrieved may support an action for
the publication of an untruth; 1 Lev. 53; 1 Sid. 79, 80; 3 Wood. 210; 2
Leon. 111; unless the assertion be made for the assertion of a supposed
claim; Com. Dig. tit. Action upon the case for Defamation, D 30; Bac. Ab.
Slander, B; but it lies if maliciously spoken. See 1 Rolle, Ab. 36 1 Saund.
243 Bac. Abr. Slander, C; 8 T. R. 130 8 East, R. 1; Stark. on Slander, 157.
     9.-Sec. 2. The charge must be false; 5 Co. 125, 6; Hob. 253; the
falsity of the accusation is to be implied till the contrary is shown. 2
East, R. 436; 1 Saund. 242. The instance of a master making an unfavorable
representation of his servant, upon an application for his character, seems
to be an exception, in that case there being a presumption from the occasion
of the speaking, that the words were true. 1 T. R. 111; 3 B. & P. 587;
Stark. on Slander, 44, 175, 223.
     10.-Sec. 3. The slander must, of course, be published, that is,
communicated to a third person; and if verbal, then in a language which he
understands, otherwise the plaintiff's reputation is not impaired. 1 Rolle,
Ab. 74; Cro. Eliz. 857; 1 Saund. 2425 n. 3; Bac. Abr. Slander, D 3. A letter
addressed to the party, containing libelous matter, is not sufficient to
maintain a civil action, though it may subject the libeler to an indictment,
as tending to a breach of the peace; 2 Bl. R. 1038; 1 T. R. 110; 1 Saund.
l32, n. 2; 4 Esp. N. P. R. 117; 2 Esp. N. P. R. 623; 2 East, R. 361; the
slander must be published respecting the plaintiff; a mother cannot maintain
an action for calling her daughter a bastard. 11 Serg. & Rawle, 343. As to
the case of a man who repeats the slander invented by another, see Stark. on
Slander, 213; 2 P. A. Bro. R. 89; 3 Yeates, 508; 3 Binn. 546.
     11.-Sec. 4. To render words actionable, they must be uttered without
legal occasion. On some occasions it is justifiable to utter slander of
another, in others it is excusable, provided it be uttered without express
malice. Bac. Ab. Slander, D 4; Rolle, Ab. 87; 1 Vin. Ab. 540. It is
justifiable for au attorney to use scandalizing expressions in support of
his client's cause and pertinent thereto. 1 M. & S. 280; 1 Holt's R. 531; 1
B. & A. 232; see 2 Serg. & Rawle, 469; 1 Binn. 178; 4 Yeates, 322; 1 P. A.
Browne's R. 40; 11 Verm. R. 536; Stark. on Slander, 182. Members of congress
and other legislative assemblies cannot be called to account for anything
said in debate.
     12.-Sec. 5. Malice is essential to the support of an action for
slanderous words. But malice is in general to be presumed until the contrary
be proved; 4 B. & C. 247; 1 Saund. 242, n. 2; 1 T. R. 1 11, 544; 1 East, R.
563; 2 East, R. 436; 2 New Rep. 335; Bull. N. P. 8; except in those cases
where the occasion prima facie excuses the publication. 4 B. & C. 247. See
14 Serg. & Rawle, 359; Stark. on Slander, 201. See, generally, Com. Dig.
tit. Action upon the case for Defamation; Bac. Abr. Slander; 1 Vin. Abr.
187; 1 Phillim. Ev. ch. 8; Yelv. 28, n.; Doctr. Plac. 53 Holt's Law of
Libels; Starkie on Slander, Ham. N. P. ch. 2, s. 3.