carpenter's rule vs ruler

carpenter's rule and ruler both are nouns.

Word	Noun	Adjective	Verb	Adverb
carpenter's rule	Yes	No	No	No
ruler	Yes	No	No	No

As nouns, ruler is a hypernym of carpenter's rule; that is, ruler is a word with a broader meaning than carpenter's rule:

carpenter's rule: a rule used by a carpenter
ruler: 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

Other hypernyms of carpenter's rule include rule.

carpenter's rule (noun)	ruler (noun)
a rule used by a carpenter	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