It is an act of cruel and unjust use of any force or power. If you force a thing to act unjustly or to act against its true nature, its real will and its inherent attitude,-that is tyranny, root and branch.
Quote: We have seen that all that is in the universe is obedient to God the creator. to obey, to live in accordance with His will and His Law or (to put it more precisely) to be a Muslim is ingrained in their very nature. God has given manpower over these things, but it is incumbent in the very nature of these things that they should be used for the fulfillment of His will and not otherwise. But one who disobeys God and resorts to kufr is the person who perpetrates the greatest injustice, for he uses all these powers of body and mind to rebel against the course of nature and becomes an unwilling instrument in the drama of disobedience. He forces his head to bow down before deities other than God and cherishes in his heart the love, reverence, and fear of other powers in utter disregard to the instinctive urge of these organs. He uses his own powers and all those things upon which he has authority against the explicit of good and thus establishes a reign of tyranny. Can there be any greater injustice, tyranny, and cruelty than that exhibited by this man who exploits and misuses everything under the sun and unscrupulously forces them to a course which affronts nature and justice? Kufr is not mere tyranny; it is, to say the least, sheer rebellion, ingratitude, and infidelity. After all, what is the reality of man? What is his power and authority?