midvein vs nervure

midvein and nervure both are nouns.

Word	Noun	Adjective	Verb	Adverb
midvein	Yes	No	No	No
nervure	Yes	No	No	No

As nouns, nervure is a hypernym of midvein; that is, nervure is a word with a broader meaning than midvein:

midvein: the vein in the center of a leaf
nervure: any of the vascular bundles or ribs that form the branching framework of conducting and supporting tissues in a leaf or other plant organ

Other hypernyms of midvein include vein.

midvein (noun)	nervure (noun)
the vein in the center of a leaf	one of the horny ribs that stiffen and support the wing of an insect
	any of the vascular bundles or ribs that form the branching framework of conducting and supporting tissues in a leaf or other plant organ