The Collaborative International Dictionary of English v.0.48:

Misfeasance \Mis*fea"sance\, n. [OF. pref. mes- wrong (L. minus
   less) + faisance doing, fr. faire to do, L. facere. Cf.
   Malfeasance.] (Law)
   A trespass; a wrong arising from an overt act; the improper
   doing of an act which a person might lawfully do. --Bouvier.
   --Wharton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

misfeasance
    n 1: doing a proper act in a wrongful or injurious manner

Moby Thesaurus II by Grady Ward, 1.0:

135 Moby Thesaurus words for "misfeasance":
   aberrancy, aberration, abuse, abuse of office, atrocity,
   bad policy, befoulment, breach, conversion, corrupt administration,
   crime, crime against humanity, criminal tendency, criminality,
   criminosis, deadly sin, debasement, defalcation, defectiveness,
   defilement, delinquency, delusion, dereliction, desecration,
   deviancy, distortion, diversion, embezzlement, enormity, errancy,
   erroneousness, error, evil, evil courses, evildoing, failure,
   fallaciousness, fallacy, falseness, falsity, fault, faultiness,
   feloniousness, felony, flaw, flawedness, fouling, genocide,
   guilty act, hamartia, heavy sin, heresy, heterodoxy, illusion,
   impolicy, impropriety, indiscretion, inexpedience, inexpediency,
   inexpiable sin, iniquity, injury, injustice, lapse, lawbreaking,
   maladministration, malefaction, malfeasance, malpractice, malum,
   malversation, minor wrong, misadministration, misapplication,
   misappropriation, misconduct, misconstruction, misdeed,
   misdemeanor, misdirection, misdoing, misemployment, misgovernment,
   misguidance, mishandling, misinterpretation, misjudgment,
   mismanagement, misprision, misprision of treason, misrule,
   misusage, misuse, mortal sin, neglect, negligence, nonfeasance,
   offense, omission, outrage, peccadillo, peccancy, peculation,
   perversion, pilfering, pollution, poor stewardship,
   positive misprision, profanation, prostitution, self-contradiction,
   sin, sin of commission, sin of omission, sinful act, sinfulness,
   slip, thou scarlet sin, tort, transgression, trespass, trip,
   unorthodoxy, untrueness, untruth, untruthfulness, unutterable sin,
   venial sin, vice, viciousness, violation, wrong, wrong conduct,
   wrongdoing, wrongness



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

MISFEASANCE, torts, contracts. The performance of an act which might
lawfully be done, in an improper manner, by which another person receives an
injury. It differs from malfeasance, (q.v.) or, nonfeasance (q.v.) Vide,
generally, 2 Vin. Ab. 35; 2 Kent, Com. 443; Doct. Pl. 62; Story, Bail. Sec.
9.
     2. It seems to be settled that there is a distinction between
misfeasance and nonfeasance in the case of mandates. In cases of
nonfeasance, the mandatary is not generally liable, because his undertaking
being gratuitous, there is no consideration to support it; but in cases of
misfeasance, the common law gives a remedy for the injury done, and to the
extent of that injury. 5 T. R. 143; 4 John. Rep. 84; Story, Bailment, Sec.
165; 2 Ld. Raym. 909, 919, 920; 2 Johns. Cas. 92; Doct. & Stu. 210; 1 Esp.
R. 74; 1 Russ. Cr. 140; Bouv. Inst. Index h.t.