grand duchy vs domain

grand duchy and domain both are nouns.

Word	Noun	Adjective	Verb	Adverb
grand duchy	Yes	No	No	No
domain	Yes	No	No	No

As nouns, domain is a hypernym of grand duchy; that is, domain is a word with a broader meaning than grand duchy:

Other hypernyms of grand duchy include demesne, land.

grand duchy (noun)	domain (noun)
the domain controlled by a grand duke or grand duchess	the content of a particular field of knowledge
	people in general; especially a distinctive group of people with some shared interest
	(mathematics) the set of values of the independent variable for which a function is defined
	territory over which rule or control is exercised
	a particular environment or walk of life