menu vs drop-down menu

menu and drop-down menu both are nouns.

Word	Noun	Adjective	Verb	Adverb
menu	Yes	No	No	No
drop-down menu	Yes	No	No	No

As nouns, drop-down menu is a hyponym of menu; that is, drop-down menu is a word with a more specific, narrower meaning than menu:

menu: (computer science) a list of options available to a computer user
drop-down menu: a menu of options that appears below the item when the computer user clicks on it

Other hyponyms of menu include cascading menu, hierarchical menu, submenu.

menu (noun)	drop-down menu (noun)
an agenda of things to do	a menu of options that appears below the item when the computer user clicks on it
a list of dishes available at a restaurant
(computer science) a list of options available to a computer user
the dishes making up a meal