The Collaborative International Dictionary of English v.0.48:

Jar \Jar\ (j[aum]r), n. [See Ajar.]
   A turn.

   Note: [Only in phrase.]
         [1913 Webster]

   On the jar, on the turn, ajar, as a door.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Jar \Jar\, v. t.
   1. To cause a short, tremulous motion of, to cause to
      tremble, as by a sudden shock or blow; to shake; to shock;
      as, to jar the earth; to jar one's faith.
      [1913 Webster]

   2. To tick; to beat; to mark or tell off. [Obs.]
      [1913 Webster]

            My thoughts are minutes, and with sighs they jar
            Their watches on unto mine eyes.      --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Jar \Jar\ (j[aum]r), n. [F. jarre, Sp. jarra, from Ar. jarrah
   ewer; cf. Pers. jarrah.]
   1. A deep, broad-mouthed vessel of earthenware or glass, for
      holding fruit, preserves, etc., or for ornamental
      purposes; as, a jar of honey; a rose jar. --Dryden.
      [1913 Webster]

   2. The measure of what is contained in a jar; as, a jar of
      oil; a jar of preserves.
      [1913 Webster]

   Bell jar, Leyden jar. See in the Vocabulary.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Jar \Jar\, n.
   1. A rattling, tremulous vibration or shock; a shake; a harsh
      sound; a discord; as, the jar of a train; the jar of harsh
      sounds.
      [1913 Webster]

   2. Clash of interest or opinions; collision; discord; debate;
      slight disagreement.
      [1913 Webster]

            And yet his peace is but continual jar. --Spenser.
      [1913 Webster]

            Cease, cease these jars, and rest your minds in
            peace.                                --Shak.
      [1913 Webster]

   3. A regular vibration, as of a pendulum.
      [1913 Webster]

            I love thee not a jar of the clock.   --Shak.
      [1913 Webster]

   4. pl. In deep well boring, a device resembling two long
      chain links, for connecting a percussion drill to the rod
      or rope which works it, so that the drill is driven down
      by impact and is jerked loose when jammed.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Jar \Jar\, v. i. [imp. & p. p. Jarred; p. pr. & vb. n.
   Jarring.] [Cf. OE. charken to creak, AS. cearcian to gnash,
   F. jars a gander, L. garrire to chatter, prate, OHG. kerran
   to chatter, croak, G. quarren to grumble, and E. jargon,
   ajar.]
   [1913 Webster]
   1. To give forth a rudely quivering or tremulous sound; to
      sound harshly or discordantly; as, the notes jarred on my
      ears.
      [1913 Webster]

            When such strings jar, what hope of harmony ?
                                                  --Shak.
      [1913 Webster]

            A string may jar in the best master's hand.
                                                  --Roscommon.
      [1913 Webster]

   2. To act in opposition or disagreement; to clash; to
      interfere; to quarrel; to dispute.
      [1913 Webster]

            When those renowned noble peers Greece
            Through stubborn pride among themselves did jar.
                                                  --Spenser.
      [1913 Webster]

            For orders and degrees
            Jar not with liberty, but well consist. --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

jar
    n 1: a vessel (usually cylindrical) with a wide mouth and
         without handles
    2: the quantity contained in a jar; "he drank a jar of beer"
       [syn: jar, jarful]
    3: a sudden jarring impact; "the door closed with a jolt"; "all
       the jars and jolts were smoothed out by the shock absorbers"
       [syn: jolt, jar, jounce, shock]
    v 1: be incompatible; be or come into conflict; "These colors
         clash" [syn: clash, jar, collide]
    2: move or cause to move with a sudden jerky motion [syn:
       jolt, jar]
    3: shock physically; "Georgia was shaken up in the Tech game"
       [syn: jar, shake up, bump around]
    4: affect in a disagreeable way; "This play jarred the audience"
    5: place in a cylindrical vessel; "jar the jam"

The Free On-line Dictionary of Computing (19 January 2023):

Java archive
jar

    (jar) A compressed archive
   file containing Java class files, filename extension:
   ".jar".  The Java Development Kit contains a tool called
   "jar" for creating .jar files, similar to the standard Unix
   tar command.  As well as archiving and compressing the Java
   class files, it also inserts a "manifest" file which can
   contain information about the class files, such as a digital
   signature.  Combining class files into a single archive file
   makes it possible to download them in a single HTTP
   transaction.  This, and the compression, speeds up execution
   of Java programs delivered via the Internet.

   (2001}-02-03)