main rotor vs rotor

main rotor and rotor both are nouns.

Word	Noun	Adjective	Verb	Adverb
main rotor	Yes	No	No	No
rotor	Yes	No	No	No

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

main rotor: rotor consisting of large rotating airfoils on a single-rotor helicopter that produce the lift to support the helicopter in the air
rotor: rotating mechanism consisting of an assembly of rotating airfoils

main rotor (noun)	rotor (noun)
rotor consisting of large rotating airfoils on a single-rotor helicopter that produce the lift to support the helicopter in the air	rotating mechanism consisting of an assembly of rotating airfoils
	the rotating armature of a motor or generator
	the revolving bar of a distributor