discussant

noun

1. Someone involved in a discussion, especially a participant in a formal discussion or who has been assigned a particular role or topic.

   “I would like to thank Cynthia Ruder, whose comments as panel discussant helped me to rework my original paper.”

   “The prominence given to readers' responses to topical issues [...] made concrete the sense of belonging to a large, active, and opinionated community of discussants.”