The Collaborative International Dictionary of English v.0.48:

dethrone \de*throne"\ (d[-e]*thr[=o]n"), v. t. [imp. & p. p.
   Dethroned (d[-e]*thr[=o]nd"); p. pr. & vb. n.
   Dethroning.] [Pref. de- + throne: cf. F. d['e]tr[^o]ner;
   pref. d['e]- (L. dis-) + tr[^o]ne throne. See Throne.]
   To remove or drive from a throne; to depose; to divest of
   supreme authority and dignity. "The Protector was dethroned."
   --Hume.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dethrone
    v 1: remove a monarch from the throne; "If the King does not
         abdicate, he will have to be dethroned" [ant: enthrone,
         throne]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "dethrone":
   break, bust, cashier, deconsecrate, defrock, depose, disbar,
   discrown, disenthrone, dismiss, displace, drum out, excommunicate,
   expel, give the gate, kick upstairs, liquidate, oust, overthrow,
   pension, pension off, purge, read out of, remove,
   remove from office, retire, strip of office, strip of rank,
   superannuate, suspend, unchurch, uncrown, unfrock, unmake,
   unsaddle, unseat, unthrone