The Collaborative International Dictionary of English v.0.48:

Depone \De*pone"\ (d[-e]*p[=o]n"), v. t. [imp. & p. p. Deponed
   (-p[=o]nd"); p. pr. & vb. n. Deponing.] [L. deponere,
   depositum, to put down, in LL., to assert under oath; de- +
   ponere to put, place. See Position, and cf. Deposit.]
   1. To lay, as a stake; to wager. [Obs.] --Hudibras.
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   2. To lay down. [R.] --Southey.
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   3. To assert under oath; to depose. [A Scotticism]
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            Sprot deponeth that he entered himself thereafter in
            conference.                           --State
                                                  Trials(1606).
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The Collaborative International Dictionary of English v.0.48:

Depone \De*pone"\, v. i.
   To testify under oath; to depose; to bear witness. [A
   Scotticism]
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         The fairy Glorians, whose credibility on this point can
         not be called in question, depones to the confinement
         of Merlin in a tree.                     --Dunlop.
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WordNet (r) 3.0 (2006):

depone
    v 1: make a deposition; declare under oath [syn: swear,
         depose, depone]