center of curvature vs midpoint

center of curvature and midpoint both are nouns.

Word	Noun	Adjective	Verb	Adverb
center of curvature	Yes	No	No	No
midpoint	Yes	No	No	No

As nouns, midpoint is a hypernym of center of curvature; that is, midpoint is a word with a broader meaning than center of curvature:

center of curvature: the center of the circle of curvature
midpoint: a point equidistant from the ends of a line or the extremities of a figure

Other hypernyms of center of curvature include center, centre.

center of curvature (noun)	midpoint (noun)
the center of the circle of curvature	a point equidistant from the ends of a line or the extremities of a figure