familiar vs well-known

familiar is a noun but well-known is not a noun.

Word	Noun	Adjective	Verb	Adverb
familiar	Yes	Yes	No	No
well-known	No	Yes	No	No

familiar (noun)	well-known (noun)
a spirit (usually in animal form) that acts as an assistant to a witch or wizard
a person attached to the household of a high official (as a pope or bishop) who renders service in return for support
a friend who is frequently in the company of another

familiar (adjective)	well-known (adjective)
well known or easily recognized	frequently experienced; known closely or intimately
within normal everyday experience; common and ordinary; not strange	widely or fully known
having mutual interests or affections; of established friendship
(usually followed by `with') well informed about or knowing thoroughly