Source : Webster's Revised Unabridged Dictionary (1913)

Tyrannous \Tyr"an*nous\, a.
   Tyrannical; arbitrary; unjustly severe; despotic. --Sir P.
   Sidney. -- {Tyr"an*nous*ly}, adv.

Source : WordNet®

tyrannous
     adj : marked by unjust severity or arbitrary behavior; "the
           oppressive government"; "oppressive laws"; "a
           tyrannical parent"; "tyrannous disregard of human
           rights" [syn: {oppressive}, {tyrannical}]