Dictionary.net

any person who exercises power in a cruel way; "his father was a tyrant"

in ancient Greece, a ruler who had seized power without legal right to it

An absolute ruler; a sovereign unrestrained by law or constitution; a usurper of sovereignty.

Specifically, a monarch, or other ruler or master, who uses power to oppress his subjects; a person who exercises unlawful authority, or lawful authority in an unlawful manner; one who by taxation, injustice, or cruel punishment, or the demand of unreasonable services, imposes burdens and hardships on those under his control, which law and humanity do not authorize, or which the purposes of government do not require; a cruel master; an oppressor.

Any one of numerous species of American clamatorial birds belonging to the family Tyrannidae; -- called also tyrant bird.

To act like a tyrant; to play the tyrant; to tyrannical.

An absolute monarch; a despot; a cruel master, who uses his power to oppress those under him.

One who uses his power oppressively: (orig.) an absolute monarch.

An arbitrary and oppressive ruler; despot; oppressor.

An arbitrary ruler; despot; oppressor.