In the dictionary, a diktat is defined as an order that is harsh and unilaterally imposed on a people without their permission. It is usually used with the connotation of being issued to a defeated country or people. A dictate is simply a command or order, without the necessity of being harsh.
The most common place to hear or read the word diktat is India, where it is used for orders which come from military or faith leaders. It still carries its pejorative connotation.
Originally, diktat came from the German language.
Examples
Following prime minister Narendra Modi’s diktat to start Swachh Bharat Mission on October 2, bureaucrats in various ministries are scrambling to get hold of brooms, dusters and dustbins. [DNA India]
With the nine-day Navratri festival round the corner in Gujarat, the Vishwa Hindu Parishad has issued a diktat not to allow Muslims at garba events and sought an apology and arrest of Mehdi Hasan Shah Baba, who had offered skullcap to Narendra Modi, for equating Hindus attending Navratri events allegedly with demons (rakshas). [Indian Express]
It can be realized only through direct negotiations with Israel, not by an international community decision or U.N. diktat. [Fox News]
Granted, it’s not a fiendishly complicated plot, though both Geller and Knight insist it’s more mature than One Day (and there is no diktat that all fiction must “challenge”). [Evening Standard]
So the people of Raqqa, by and large, are forced to toe the line and follow the diktats of their new rulers. [CBS News]