ruler vs meterstick

ruler and meterstick both are nouns.

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

As nouns, meterstick is a hyponym of ruler; that is, meterstick is a word with a more specific, narrower meaning than ruler:

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
meterstick: a rule one meter long (usually marked off in centimeters and millimeters)

Other hyponyms of ruler include carpenter's rule, foot rule, metrestick, yard measure, yardstick.

ruler (noun)	meterstick (noun)
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 rule one meter long (usually marked off in centimeters and millimeters)
a person who rules or commands