Supposedly/səˈpəʊzɪdli/ Definition 1 of 2Pro Tip 1/3Uncertainty Use 'supposedly' when something is widely accepted but lacking solid proof. Tom is supposedly a great singer, but I've never heard him. Pro Tip 2/3Common Belief It suggests what is generally believed to be the case, even if it's not verified. Dinosaurs are supposedly ancestors of birds. Pro Tip 3/3Hearsay Usage Often used to report information heard from others, not first-hand knowledge. She's supposedly moved to a new city, according to rumors.