rotor head vs axis

rotor head and axis both are nouns.

Word	Noun	Adjective	Verb	Adverb
rotor head	Yes	No	No	No
axis	Yes	No	No	No

As nouns, axis is a hypernym of rotor head; that is, axis is a word with a broader meaning than rotor head:

Other hypernyms of rotor head include axis of rotation.

rotor head (noun)	axis (noun)
the axis around which the major rotor of a helicopter turns	the center around which something rotates
	the 2nd cervical vertebra; serves as a pivot for turning the head
	a straight line through a body or figure that satisfies certain conditions
	a group of countries in special alliance
	the main stem or central part about which plant organs or plant parts such as branches are arranged