The Collaborative International Dictionary of English v.0.48:
Tyrannous \Tyr"an*nous\ (t[i^]r"an*n[u^]s), a. Tyrannical; arbitrary; unjustly severe; despotic. --Sir P. Sidney. -- Tyr"an*nous*ly, adv. [1913 Webster]WordNet (r) 3.0 (2006):
tyrannous adj 1: marked by unjust severity or arbitrary behavior; "the oppressive government"; "oppressive laws"; "a tyrannical parent"; "tyrannous disregard of human rights" [syn: oppressive, tyrannical, tyrannous]