menu vs submenu

menu and submenu both are nouns.

Word	Noun	Adjective	Verb	Adverb
menu	Yes	No	No	No
submenu	Yes	No	No	No

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

menu: (computer science) a list of options available to a computer user
submenu: a secondary menu that appears while you are holding the cursor over an item on the primary menu

Other hyponyms of menu include drop-down menu, cascading menu, hierarchical menu.

menu (noun)	submenu (noun)
an agenda of things to do	a secondary menu that appears while you are holding the cursor over an item on the primary menu
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