cocktail vs appetizer

cocktail and appetizer both are nouns.

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

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

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

Other hypernyms of cocktail include appetiser, starter.

cocktail (noun)	appetizer (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