The Collaborative International Dictionary of English v.0.48:

Misprision \Mis*pri"sion\, n. [LL. misprisio, or OF. mesprison,
   prop., a mistaking, but confused with OF. mespris contempt,
   F. m['e]pris. See 2d Misprise, Misprize, Prison.]
   [1913 Webster]
   1. The act of misprising; misapprehension; misconception;
      mistake. [Archaic] --Fuller.
      [1913 Webster]

            The misprision of this passage has aided in
            fostering the delusive notion.        --Hare.
      [1913 Webster]

   2. Neglect; undervaluing; contempt. [Obs.] --Shak.
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   3. (Law) A neglect, negligence, or contempt.
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   Note: In its larger and older sense it was used to signify
         "every considerable misdemeanor which has not a certain
         name given to it in the law." --Russell.
         In a more modern sense it is applied exclusively to two
         offenses:
         1.

   Misprision of treason, which is omission to notify the
      authorities of an act of treason by a person cognizant
      thereof. --Stephen.
      2.

   Misprision of felony, which is a concealment of a felony by
      a person cognizant thereof. --Stephen.
      [1913 Webster]

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

MISPRISION, crim. law. 1. In its larger sense, this word is used to signify
every considerable misdemeanor, which has not a certain name given to it in
the law; and it is said that a misprision is contained in every treason or
felony whatever. 2. In its narrower sense it is the concealment of a crime.
     2. Misprision of treason, is the concealment of treason, by being
merely passive; Act of Congress of April 30, 1790, 1 Story's L. U. S. 83; 1
East, P. C. 139; for if any assistance be given, to the traitor, it makes
the party a principal, as there is no accessories in treason.
     3. Misprision of felony, is the like concealment of felony, without
giving any degree of maintenance to the felon; Act of Congress of April 30,
1790, s. 6, 1 Story's L. U. S. 84; for if any aid be given him, the party
becomes an accessory after the fact.
     4. It is the duty of every good citizen, knowing of a treason or felony
having been committed; to inform a magistrate. Silently to observe the
commission of a felony, without using any endeavors to apprehend the
offender, is a misprision. 1 Russ. on Cr. 43; Hawk. P. C. c. 59, s. 6; Id.
Book 1, c. s. 1; 4 Bl. Com. 119.
     5. Misprisions which are merely positive, are denominated contempts or
high misdemeanors; as, for example, dissuading a witness from giving
evidence. 4 Bl. Com. 126.