lava vs aa

lava and aa both are nouns.

Word	Noun	Adjective	Verb	Adverb
lava	Yes	No	No	No
aa	Yes	No	No	No

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

lava: rock that in its molten form (as magma) issues from volcanoes; lava is what magma is called when it reaches the surface
aa: a dry form of lava resembling clinkers

Other hyponyms of lava include pahoehoe, pillow lava.

lava (noun)	aa (noun)
rock that in its molten form (as magma) issues from volcanoes; lava is what magma is called when it reaches the surface	a dry form of lava resembling clinkers