onlookerEnglishOxford English Thesaurusonlooker noun an onlooker described the scene as one of utter devastation: eyewitness, witness, observer, looker-on, fly on the wall, spectator, watcher, viewer, sightseer, bystander, non-participant; informal rubberneck; literary beholder. ▷antonyms participant.onlooker Oxford Dictionary of English