[countable] an instrument for measuring and showing time, in a room, on the wall of a building or on a computer screen (not worn or carried like a watch) It was ten past six by the kitchen clock. The clock struck twelve/midnight. The clock is fast/slow. The clock has stopped. the clock face (= the front part of a clock with the numbers on) The hands of the clock crept slowly around. Ellen heard the loud ticking of the clock in the hall.