participant vs attender

participant and attender both are nouns.

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

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

participant (noun)	attender (noun)
someone who takes part in an activity	someone who waits on or tends to or attends to the needs of another
a person who participates in or is skilled at some game	a person who is present and participates in a meeting
	someone who listens attentively