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.]
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   1. To give forth a rudely quivering or tremulous sound; to
      sound harshly or discordantly; as, the notes jarred on my
      ears.
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            When such strings jar, what hope of harmony ?
                                                  --Shak.
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            A string may jar in the best master's hand.
                                                  --Roscommon.
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   2. To act in opposition or disagreement; to clash; to
      interfere; to quarrel; to dispute.
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            When those renowned noble peers Greece
            Through stubborn pride among themselves did jar.
                                                  --Spenser.
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            For orders and degrees
            Jar not with liberty, but well consist. --Milton.
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