bottle gourd vs gourd

bottle gourd and gourd both are nouns.

Word	Noun	Adjective	Verb	Adverb
bottle gourd	Yes	No	No	No
gourd	Yes	No	No	No

As nouns, gourd is a hypernym of bottle gourd; that is, gourd is a word with a broader meaning than bottle gourd:

bottle gourd: Old World climbing plant with hard-shelled bottle-shaped gourds as fruits
gourd: any vine of the family Cucurbitaceae that bears fruits with hard rinds

Other hypernyms of bottle gourd include gourd vine.

bottle gourd (noun)	gourd (noun)
Old World climbing plant with hard-shelled bottle-shaped gourds as fruits	bottle made from the dried shell of a bottle gourd
	any vine of the family Cucurbitaceae that bears fruits with hard rinds
	any of numerous inedible fruits with hard rinds