kidnaper vs crook

kidnaper and crook both are nouns.

Word	Noun	Adjective	Verb	Adverb
kidnaper	Yes	No	No	No
crook	Yes	No	Yes	No

As nouns, crook is a hypernym of kidnaper; that is, crook is a word with a broader meaning than kidnaper:

kidnaper: someone who unlawfully seizes and detains a victim (usually for ransom)
crook: someone who has committed a crime or has been legally convicted of a crime

Other hypernyms of kidnaper include captor, capturer, criminal, felon, malefactor, outlaw.

kidnaper (noun)	crook (noun)
someone who unlawfully seizes and detains a victim (usually for ransom)	a long staff with one end being hook shaped
	someone who has committed a crime or has been legally convicted of a crime
	a circular segment of a curve

kidnaper (verb)	crook (verb)
	bend or cause to bend