regent vs ruler

regent and ruler both are nouns.

Word	Noun	Adjective	Verb	Adverb
regent	Yes	Yes	No	No
ruler	Yes	No	No	No

As nouns, ruler is a hypernym of regent; that is, ruler is a word with a broader meaning than regent:

regent: someone who rules during the absence or incapacity or minority of the country's monarch
ruler: a person who rules or commands

Other hypernyms of regent include swayer.

regent (noun)	ruler (noun)
someone who rules during the absence or incapacity or minority of the country's monarch	measuring stick consisting of a strip of wood or metal or plastic with a straight edge that is used for drawing straight lines and measuring lengths
members of a governing board	a person who rules or commands

regent (adjective)	ruler (adjective)
acting or functioning as a regent or ruler