hierarchical menu vs submenu

hierarchical menu and submenu both are nouns.

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

As nouns, hierarchical menu and submenu are synonyms defined as:

hierarchical menu and submenu: a secondary menu that appears while you are holding the cursor over an item on the primary menu

Other synonyms of hierarchical menu include cascading menu.

hierarchical menu (noun)	submenu (noun)
a secondary menu that appears while you are holding the cursor over an item on the primary menu	a secondary menu that appears while you are holding the cursor over an item on the primary menu