kidnapper vs captor

kidnapper and captor both are nouns.

Word	Noun	Adjective	Verb	Adverb
kidnapper	Yes	No	No	No
captor	Yes	No	No	No

As nouns, captor is a hypernym of kidnapper; that is, captor is a word with a broader meaning than kidnapper:

kidnapper: someone who unlawfully seizes and detains a victim (usually for ransom)
captor: a person who captures and holds people or animals

Other hypernyms of kidnapper include capturer, criminal, crook, felon, malefactor, outlaw.

kidnapper (noun)	captor (noun)
someone who unlawfully seizes and detains a victim (usually for ransom)	a person who captures and holds people or animals