hors d'oeuvre vs appetiser

hors d'oeuvre and appetiser both are nouns.

Word	Noun	Adjective	Verb	Adverb
hors d'oeuvre	Yes	No	No	No
appetiser	Yes	No	No	No

As nouns, appetiser is a hypernym of hors d'oeuvre; that is, appetiser is a word with a broader meaning than hors d'oeuvre:

hors d'oeuvre: a dish served as an appetizer before the main meal
appetiser: food or drink to stimulate the appetite (usually served before a meal or as the first course)

Other hypernyms of hors d'oeuvre include appetizer, starter.

hors d'oeuvre (noun)	appetiser (noun)
a dish served as an appetizer before the main meal	food or drink to stimulate the appetite (usually served before a meal or as the first course)