wallboard vs fiberboard

wallboard and fiberboard both are nouns.

Word	Noun	Adjective	Verb	Adverb
wallboard	Yes	No	No	No
fiberboard	Yes	No	No	No

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

wallboard: a wide flat board used to cover walls or partitions; made from plaster or wood pulp or other materials and used primarily to form the interior walls of houses
fiberboard: wallboard composed of wood chips or shavings bonded together with resin and compressed into rigid sheets

Other hyponyms of wallboard include beaver board, fibreboard, particle board, gypsum board, plasterboard.

wallboard (noun)	fiberboard (noun)
a wide flat board used to cover walls or partitions; made from plaster or wood pulp or other materials and used primarily to form the interior walls of houses	wallboard composed of wood chips or shavings bonded together with resin and compressed into rigid sheets