The Collaborative International Dictionary of English v.0.48:

Malicious \Ma*li"cious\, a. [Of. malicius, F. malicieux, fr. L.
   malitiosus. See Malice.]
   1. Indulging or exercising malice; harboring ill will or
      enmity.
      [1913 Webster]

            I grant him bloody, . . .
            Sudden, malicious, smacking of every sin
            That has a name.                      --Shak.
      [1913 Webster]

   2. Proceeding from hatred or ill will; dictated by malice;
      as, a malicious report; malicious mischief.
      [1913 Webster]

   3. (Law) With wicked or mischievous intentions or motives;
      wrongful and done intentionally without just cause or
      excuse; as, a malicious act.
      [1913 Webster]

   Malicious abandonment, the desertion of a wife or husband
      without just cause. --Burrill.

   Malicious prosecution or Malicious arrest (Law), a wanton
      prosecution or arrest, by regular process in a civil or
      criminal proceeding, without probable cause. --Bouvier.
      [1913 Webster]

   Syn: Ill-disposed; evil-minded; mischievous; envious;
        malevolent; invidious; spiteful; bitter; malignant;
        rancorous; malign.
        [1913 Webster] -- Ma*li"cious*ly, adv. --
        Ma*li"cious*ness, n.
        [1913 Webster]

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

MALICIOUS PROSECUTION, or MALICIOUS ARREST, torts, or remedies. These terms
import a wanton prosecution or arrest, made by a prosecutor in a criminal
proceeding, or a plaintiff in a civil suit, without probable cause, by a
regular process and proceeding, which the facts did not warrant, as appears
by the result.
     2. This definition will be analysed by considering, 1. The nature of
the prosecution or arrest. 2. Who is liable under it. 3. What are malice and
probable cause. 4. The proceedings. 5. The result of the prosecution and
afterwards, 6. The remedy.
     3.-Sec. 1. Where the defendant commenced a criminal prosecution
wantonly and in other respects against law, he will be responsible. Addis.
R. 270; 12 Conn. 219. The prosecution of a civil suit, when malicious, is a
good cause of action, even when there has been no arrest. 1 P. C. C. 210; 11
Conn. 582; 1 Wend. 345. But no action lies for commencing a civil action,
though without sufficient cause. 1 Penna. R. 235.
     4.-Sec. 2. The action lies against the prosecutor and even against a
mere informer, when the proceedings are malicious. 5 Stew. & Port. 367. But
grand jurors are not liable to an action for a malicious prosecution, for
information given by them to their fellow jurors, on which a prosecution is
founded. Hardin, 556. Such action lies against a plaintiff in a civil action
who maliciously sues out the writ and prosecutes it; 16 Pick. 453; but an
action does not lie against an attorney at law for bringing the action, when
regularly employed. 16 Pick. 478. See 6 Pick. 193.
     5.-Sec. 3. There must be malice and want of probable cause. 1 Wend.
140, 345; 7 Cowen, 281; 2 P. A. Browne, Appx. xlii; Cooke, 90; Litt. Sel.
Cas. 106; 4 Litt. 334; 3 Gil. & John. 377; 1 N. & M. 36; 12 Conn. 219; 3
Call. 446; 2 Hall, 315; 3 Mason, 112, 2 N. & M. 54,143. See Malice; Probable
cause.
     6.-Sec. 4. The Proceedings under which the original prosecution or
action was held, must have been regular, in the ordinary course of justice,
and before a tribunal having power to ascertain the truth or falsity of the
charge, and to punish the supposed offender, the now plaintiff. 3 Pick. 379,
383. When the proceedings are irregular, the prosecutor is a trespasser. 3
Blackf. 210. See Regular and irregular process.
     7.-Sec. 5. The malicious prosecution or action must be ended, and the
plaintiff must show it was groundless, either by his acquittal or by
obtaining a final judgment in his favor in a civil action. 1 Root, R. 553; 1
N. & M. 36; 2 N. & M. 54, 143; 7 Cowen, 715; 2 Dev. & Bat. 492.
     8.-Sec. 6. The remedy for a malicious prosecution is an action on the
case to recover damages for the injury sustained. 5 Stew. & Porter, 367; 2
Conn. 700; 11 Mass 500; 6 Greenl. 421; 3 Gill. & John. 377. See Case;
Regular and irregular process.
     See, generally, Bull. N. P. 11; 1 Saund. 228; 12 Mod. 208; 1 T. R. 493
to 551;  Bac. Ab. Actions on the case, H; Bouv. Inst. Index, h.t.