cocktail vs appetiser

cocktail and appetiser both are nouns.

Word	Noun	Adjective	Verb	Adverb
cocktail	Yes	No	No	No
appetiser	Yes	No	No	No

As nouns, appetiser is a hypernym of cocktail; that is, appetiser is a word with a broader meaning than cocktail:

cocktail: an appetizer served as a first course at a meal
appetiser: food or drink to stimulate the appetite (usually served before a meal or as the first course)

Other hypernyms of cocktail include appetizer, starter.

cocktail (noun)	appetiser (noun)
a short mixed drink	food or drink to stimulate the appetite (usually served before a meal or as the first course)
an appetizer served as a first course at a meal