The Collaborative International Dictionary of English v.0.48:
dethronement \de*throne"ment\, n. [Cf. F. d['e]tr[^o]nement.] Deposal from a throne; deposition from regal power. [1913 Webster]WordNet (r) 3.0 (2006):
dethronement n 1: the act of deposing someone; removing a powerful person from a position or office [syn: deposition, dethronement]