lava vs pillow lava

lava and pillow lava both are nouns.

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

As nouns, pillow lava is a hyponym of lava; that is, pillow lava 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
pillow lava: lava that hardened in rounded shapes suggestive of pillows; believed to result from underwater eruptions

Other hyponyms of lava include aa, pahoehoe.

lava (noun)	pillow lava (noun)
rock that in its molten form (as magma) issues from volcanoes; lava is what magma is called when it reaches the surface	lava that hardened in rounded shapes suggestive of pillows; believed to result from underwater eruptions