executioner vs slayer

executioner and slayer both are nouns.

Word	Noun	Adjective	Verb	Adverb
executioner	Yes	No	No	No
slayer	Yes	No	No	No

As nouns, slayer is a hypernym of executioner; that is, slayer is a word with a broader meaning than executioner:

executioner: an official who inflicts capital punishment in pursuit of a warrant
slayer: someone who causes the death of a person or animal

Other hypernyms of executioner include killer.

executioner (noun)	slayer (noun)
an official who inflicts capital punishment in pursuit of a warrant	someone who causes the death of a person or animal