Sistrurus miliaris vs rattler

Sistrurus miliaris and rattler both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sistrurus miliaris	Yes	No	No	No
rattler	Yes	No	No	No

As nouns, rattler is a hypernym of Sistrurus miliaris; that is, rattler is a word with a broader meaning than Sistrurus miliaris:

Sistrurus miliaris: small pygmy rattlesnake
rattler: pit viper with horny segments at the end of the tail that rattle when shaken

Other hypernyms of Sistrurus miliaris include rattlesnake.

Sistrurus miliaris (noun)	rattler (noun)
small pygmy rattlesnake	pit viper with horny segments at the end of the tail that rattle when shaken
	a railroad train consisting of freight cars