The Collaborative International Dictionary of English v.0.48:

Oath \Oath\ ([=o]th), n.; pl. Oaths ([=o][th]z). [OE. othe,
   oth, ath, AS. [=a][eth]; akin to D. eed, OS. [=e][eth], G.
   eid, Icel. ei[eth]r, Sw. ed, Dan. eed, Goth. ai[thorn]s; cf.
   OIr. oeth.]
   1. A solemn affirmation or declaration, made with a reverent
      appeal to God for the truth of what is affirmed. "I have
      an oath in heaven" --Shak.
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            An oath of secrecy for the concealing of those
            [inventions] which we think fit to keep secret.
                                                  --Bacon.
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   2. A solemn affirmation, connected with a sacred object, or
      one regarded as sacred, as the temple, the altar, the
      blood of Abel, the Bible, the Koran, etc.
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   3. (Law) An appeal (in verification of a statement made) to a
      superior sanction, in such a form as exposes the party
      making the appeal to an indictment for perjury if the
      statement be false.
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   4. A careless and blasphemous use of the name of the divine
      Being, or anything divine or sacred, by way of appeal or
      as a profane exclamation or ejaculation; an expression of
      profane swearing. "A terrible oath" --Shak.
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