methanogen vs archaebacterium

methanogen and archaebacterium both are nouns.

Word	Noun	Adjective	Verb	Adverb
methanogen	Yes	No	No	No
archaebacterium	Yes	No	No	No

As nouns, archaebacterium is a hypernym of methanogen; that is, archaebacterium is a word with a broader meaning than methanogen:

methanogen: archaebacteria found in anaerobic environments such as animal intestinal tracts or sediments or sewage and capable of producing methane; a source of natural gas
archaebacterium: considered ancient life forms that evolved separately from bacteria and blue-green algae

Other hypernyms of methanogen include archaebacteria, archaeobacteria, archeobacteria.

methanogen (noun)	archaebacterium (noun)
archaebacteria found in anaerobic environments such as animal intestinal tracts or sediments or sewage and capable of producing methane; a source of natural gas	considered ancient life forms that evolved separately from bacteria and blue-green algae