bootlicker vs ass-kisser

bootlicker and ass-kisser both are nouns.

Word	Noun	Adjective	Verb	Adverb
bootlicker	Yes	No	No	No
ass-kisser	Yes	No	No	No

As nouns, ass-kisser is a hypernym of bootlicker; that is, ass-kisser is a word with a broader meaning than bootlicker:

bootlicker: someone who humbles himself as a sign of respect; who behaves as if he had no self-respect
ass-kisser: a person who tries to please someone in order to gain a personal advantage

Other hypernyms of bootlicker include crawler, lackey, sycophant, toady.

bootlicker (noun)	ass-kisser (noun)
someone who humbles himself as a sign of respect; who behaves as if he had no self-respect	a person who tries to please someone in order to gain a personal advantage