caliph vs ruler

caliph and ruler both are nouns.

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

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

caliph: the civil and religious leader of a Muslim state considered to be a representative of Allah on earth
ruler: a person who rules or commands

Other hypernyms of caliph include Moslem, Muslim, swayer.

caliph (noun)	ruler (noun)
the civil and religious leader of a Muslim state considered to be a representative of Allah on earth	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
	a person who rules or commands