audience vs readership

audience and readership both are nouns.

Word	Noun	Adjective	Verb	Adverb
audience	Yes	No	No	No
readership	Yes	No	No	No

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

audience: the part of the general public interested in a source of information, entertainment, or a product/service
readership: the audience reached by written communications (books or magazines or newspapers etc.)

Other hyponyms of audience include TV audience, viewers, viewing audience, listenership.

audience (noun)	readership (noun)
a conference (usually with someone important)	the audience reached by written communications (books or magazines or newspapers etc.)
a gathering of spectators or listeners at a (usually public) performance
the part of the general public interested in a source of information, entertainment, or a product/service
an opportunity to state your case and be heard