domain vs grand duchy

domain and grand duchy both are nouns.

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

As nouns, grand duchy is a hyponym of domain; that is, grand duchy is a word with a more specific, narrower meaning than domain:

domain (noun)	grand duchy (noun)
the content of a particular field of knowledge	the domain controlled by a grand duke or grand duchess
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