The Collaborative International Dictionary of English v.0.48:

Petit \Pet"it\ (p[e^]t"[y^]; F. pe*t[-e]"), a. [F. See Petty.]
   Small; little; insignificant; mean; -- Same as Petty.
   [Obs., except in legal language.]
   [1913 Webster]

         By what small, petit hints does the mind catch hold of
         and recover a vanishing notion.          --South.
   [1913 Webster]

   Petit constable, an inferior civil officer, subordinate to
      the high constable.

   Petit jury, a jury of twelve men, impaneled to try causes
      at the bar of a court; -- so called in distinction from
      the grand jury.

   Petit larceny, the stealing of goods of, or under, a
      certain specified small value; -- opposed to grand
      larceny. The distinction is abolished in England.

   Petit ma[^i]tre. [F., lit., little master.] A fop; a
      coxcomb; a ladies' man. --Goldsmith.

   Petit serjeanty (Eng. Law), the tenure of lands of the
      crown, by the service of rendering annually some implement
      of war, as a bow, an arrow, a sword, a flag, etc.

   Petit treason, formerly, in England, the crime of killing a
      person to whom the offender owed duty or subjection, as
      one's husband, master, mistress, etc. The crime is now not
      distinguished from murder.
      [1913 Webster]

WordNet (r) 3.0 (2006):

petit jury
    n 1: a jury of 12 to determine the facts and decide the issue in
         civil or criminal proceedings [syn: petit jury, petty
         jury]