noun

• (historical, Ancient Greece) A usurper; one who gains power and rules extralegally, distinguished from kings elevated by election or succession.
  "To proue him Tyrant, this reason may suffice, That Henry liueth still."
• (obsolete) Any monarch or governor.
  "Cassius... set tyrants over all Syria."
• (by extension) Any person who abuses the power of position or office to treat others unjustly, cruelly, or harshly.
  "A plague vpon the Tyrant that I serue"
• (by extension) A villain; a person or thing who uses strength or violence to treat others unjustly, cruelly, or harshly.
  "I was a blasphemar, and a persecuter, and a tyraunt."

adj

• (uncommon) Tyrannical, tyrannous; like, characteristic of, or in the manner of a tyrant.
  "He was most tirant & cruell of all emperours."

verb

• (intransitive, obsolete) To act like a tyrant; to be tyrannical.
  "Let thy judgment be king, but not tyrant over it"
• (transitive, obsolete) To tyrannize.