a person or thing that times.

a person who measures or records time.

a device for indicating or measuring elapsed time, as a stopwatch.

a device for controlling machinery, appliances, or the like, in a specified way at a predetermined time

Please put the roast in the oven and set the timer to cook it for two hours.

(in an internal-combustion engine) a set of points actuated by a cam, which causes the spark for igniting the charge at the instant required.