kidnapper vs seizer

kidnapper and seizer both are nouns.

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

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

kidnapper: someone who unlawfully seizes and detains a victim (usually for ransom)
seizer: a kidnapper who drugs men and takes them for compulsory service aboard a ship

Other hyponyms of kidnapper include crimp, crimper, shanghaier.

kidnapper (noun)	seizer (noun)
someone who unlawfully seizes and detains a victim (usually for ransom)	a kidnapper who drugs men and takes them for compulsory service aboard a ship