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]

Moby Thesaurus II by Grady Ward, 1.0:

217 Moby Thesaurus words for "jar":
   Babel, Discordia, Eris, agitate, agitation, agree to disagree, bag,
   barrel, basket, be at cross-purposes, be at variance, belch, blare,
   blat, bob, bobble, bottle, bounce, bowl down, bowl over, box,
   box up, bray, break, break off, bump, burr, buzz, cackle, calabash,
   can, canteen, capsule, carafe, carboy, carton, case, cask, caster,
   caw, chatter, chirr, clamor, clang, clangor, clank, clash,
   clashing, collide, collision, concussion, conflict, contention,
   contradict, counter, crash, crate, craunch, croak, cruet, crump,
   crunch, cruse, decanter, demijohn, didder, differ,
   differ in opinion, disaccord, disaffinity, disagree,
   discombobulate, discompose, disconcert, discord, discordance,
   discordancy, disharmony, disquiet, dissent, disturb, disturbance,
   dither, do up, electrify, encase, encyst, enmity, ewer, falter,
   fifth, flacon, flagon, flask, flasket, fluctuation, flurry,
   fluster, flutter, friction, frighten, fuss, gourd, grate, grate on,
   grimace, grind, groan, growl, grumble, hamper, harshness,
   have an ague, hipflask, hit a clinker, hold opposite views,
   hot-water bottle, hustle, incompatibility, incompatibleness,
   inharmoniousness, inharmony, irritate, jactitate, jangle,
   jangle the nerves, jar on, jerk, jeroboam, jig, jigget, jiggle,
   jog, joggle, jolt, jostle, jounce, jug, jump, lota, magnum,
   mere noise, mischief, mismatch, mismate, misunderstand one another,
   mussuk, negate, noise, noncooperation, not get along, object, olla,
   open conflict, pack, package, parcel, perturb, phial, pot,
   pull different ways, put on edge, put up, quake, quaver, quiver,
   rasp, rattle, rictus, rock, rub, ruffle, sack, scranch, scrape,
   scratch, scrunch, shake, shake up, shiver, shock, shudder, smash,
   snarl, snore, stagger, start, startle, stir, stoup,
   strained relations, stun, sway, take aback, tank, tension, tic,
   tin, tremble, tremor, trouble, turn, twang, twitch, twitter,
   unharmoniousness, unpleasantness, unsettle, unstring, untune,
   upset, vacuum bottle, vary, vial, vibrate, vibration, wobble



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

JAR
       Java ARchive (Java)