companion vs attender

companion and attender both are nouns.

Word	Noun	Adjective	Verb	Adverb
companion	Yes	No	Yes	No
attender	Yes	No	No	No

As nouns, attender is a hypernym of companion; that is, attender is a word with a broader meaning than companion:

companion: one paid to accompany or assist or live with another
attender: someone who waits on or tends to or attends to the needs of another

Other hypernyms of companion include attendant, tender.

companion (noun)	attender (noun)
a friend who is frequently in the company of another	someone who waits on or tends to or attends to the needs of another
one paid to accompany or assist or live with another	a person who is present and participates in a meeting
a traveler who accompanies you	someone who listens attentively

companion (verb)	attender (verb)
be a companion to somebody