Nouns:
* Empire: (The most common form)
* Empires: (Plural form)
* Imperialism: (The practice of expanding an empire)
* Imperialist: (A person who advocates for imperialism)
* Empress: (A female sovereign who rules an empire)
* Emperor: (A male sovereign who rules an empire)
Adjectives:
* Imperial: (Relating to an empire)
* Empiric: (Based on observation or experiment)
* Empress: (Relating to an empress)
* Emperor: (Relating to an emperor)
Verbs:
* Emperorised: (To rule over an empire) - This word is rarely used, but it exists.
Other related words:
* Colonialism: (The practice of establishing colonies and controlling them)
* Colony: (A territory that is under the control of another country)
* Dominion: (A territory under the control of a sovereign power)
* Sovereignty: (The supreme power or authority in a state)
The specific word forms used will depend on the context of your writing.