guesstimate /ˈɡɛs.təˌmeɪt/verb 2/ˈɡɛs.tə.mət/ noun 1forms 3 verb2 •To make a guesstimate. •To make a guesstimate of a specific quantity. guesstimate /ˈɡɛs.tə.mət/ noun1 •(informal) An estimate that is hardly any better than a guess, often because it is based on insufficient or unreliable data.I'm not sure how many people were at the festival. My best guesstimate is 50,000. formsguesstimated · guesstimating · guesstimates