ques ‧ tion ‧ er /ˈkwestʃ ə nə $ -ər/ BrE AmE noun [countable]
[ Word Family: noun : ↑ question , questioning, ↑ questioner , ↑ questionnaire ; adjective : ↑ questionable ≠ ↑ unquestionable , ↑ questioning ≠ ↑ unquestioning , ↑ unquestioned ; adverb : ↑ unquestionably , ↑ questioningly ≠ ↑ unquestioningly ; verb : ↑ question ]
someone who is asking a question, for example in a public discussion