captor vs kidnapper

captor and kidnapper both are nouns.

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

As nouns, kidnapper is a hyponym of captor; that is, kidnapper is a word with a more specific, narrower meaning than captor:

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

Other hyponyms of captor include abductor, kidnaper, snatcher, surpriser.

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