underestimateun·der·es·ti·mate /ˌʌndərˈestɪmeɪt/ verb [transitiveT] to think that something is smaller than it really isWe underestimated our operating costs.
The official statistics seriously underestimate actual unemployment.
—underestimate /ˌʌndərˈestəmət/ noun [countableC]These unemployment figures should be regarded as underestimates.