One that participates, shares, or takes part in something.(noun)
Sharing in or taking part; participating.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "participant" in a sentence
"From the still, neither participant is an advertisement for blogging as a healthy lifestyle."
"The other participant is my husband, novelist Gordon Aalborg."
"That being said, I would add a question asking if the participant is currently in school and if so what level of education it is."