Participant
late Middle English: from Latin participant-, literally ‘sharing in’, from the verb participare (see participate).
wiktionary
Borrowed from Middle French participant, from Latin participāns, present participle of participō; see participate.
etymonline
participant (adj.)
"sharing, having a share or part," late 15c., from Old French participant and directly from Latin participantem (nominative participans), present participle of participare "to share in, partake of," from particeps "sharing, partaking" (see participation).
participant (n.)
"one who participates, a partaker," 1560s, from French participant, from Latin participantem (nominative participans), present participle of participare "to share in, partake of" from particeps "sharing, partaking" (see participation).