The Collaborative International Dictionary of English v.0.48:

Rival \Ri"val\, v. t. [imp. & p. p. Rivaledor Rivalled; p.
   pr. & vb. n. Rivaling or Rivalling.]
   1. To stand in competition with; to strive to gain some
      object in opposition to; as, to rival one in love.
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   2. To strive to equal or exel; to emulate.
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            To rival thunder in its rapid course. --Dryden.
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The Collaborative International Dictionary of English v.0.48:

Rival \Ri"val\, v. i.
   To be in rivalry. [Obs.] --Shak.
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The Collaborative International Dictionary of English v.0.48:

Rival \Ri"val\, a.
   Having the same pretensions or claims; standing in
   competition for superiority; as, rival lovers; rival claims
   or pretensions.
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         The strenuous conflicts and alternate victories of two
         rival confederacies of statesmen.        --Macaulay.
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The Collaborative International Dictionary of English v.0.48:

Rival \Ri"val\, n. [F. rival (cf. It. rivale), L. rivales two
   neigbors having the same brook in common, rivals, fr. rivalis
   belonging to a brook, fr. rivus a brook. Cf. Rivulet,
   Rete.]
   1. A person having a common right or privilege with another;
      a partner. [Obs.]
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            If you do meet Horatio and Marcellus,
            The rivals of my watch, bid them make haste. --Shak.
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   2. One who is in pursuit of the same object as another; one
      striving to reach or obtain something which another is
      attempting to obtain, and which one only can posses; a
      competitor; as, rivals in love; rivals for a crown.
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   Note: "Rivals, in the primary sense of the word, are those
         who dwell on the banks of the same stream. But since,
         as all experience shows, there is no such fruitful
         source of coutention as a water right, it would
         continually happen that these occupants of the opposite
         banks would be at strife with one another in regard of
         the periods during which they severally had a right to
         the use of the stream . . . And thus 'rivals' . . .
         came to be used of any who were on any grounds in more
         or less unfriendly competition with one another."
         --Trench.
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   Syn: Competitor; emulator; antagonist.
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WordNet (r) 3.0 (2006):

rival
    n 1: the contestant you hope to defeat; "he had respect for his
         rivals"; "he wanted to know what the competition was doing"
         [syn: rival, challenger, competitor, competition,
         contender]
    v 1: be equal to in quality or ability; "Nothing can rival
         cotton for durability"; "Your performance doesn't even
         touch that of your colleagues"; "Her persistence and
         ambition only matches that of her parents" [syn: equal,
         touch, rival, match]
    2: be the rival of, be in competition with; "we are rivaling for
       first place in the race"