virus vs bacteriophage

virus and bacteriophage both are nouns.

Word	Noun	Adjective	Verb	Adverb
virus	Yes	No	No	No
bacteriophage	Yes	No	No	No

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

virus: (virology) ultramicroscopic infectious agent that replicates itself only within cells of living hosts; many are pathogenic; a piece of nucleic acid (DNA or RNA) wrapped in a thin coat of protein
bacteriophage: a virus that is parasitic (reproduces itself) in bacteria

Other hyponyms of virus include arborvirus, arbovirus, phage, plant virus, animal virus, slow virus, tumor virus, vector.

virus (noun)	bacteriophage (noun)
(virology) ultramicroscopic infectious agent that replicates itself only within cells of living hosts; many are pathogenic; a piece of nucleic acid (DNA or RNA) wrapped in a thin coat of protein	a virus that is parasitic (reproduces itself) in bacteria
a software program capable of reproducing itself and usually capable of causing great harm to files or other programs on the same computer
a harmful or corrupting agency