attacker vs ambusher

attacker and ambusher both are nouns.

Word	Noun	Adjective	Verb	Adverb
attacker	Yes	No	No	No
ambusher	Yes	No	No	No

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

attacker: someone who attacks
ambusher: an attacker who waits in a concealed position to launch a surprise attack

attacker (noun)	ambusher (noun)
someone who attacks	an attacker who waits in a concealed position to launch a surprise attack