A person or thing that cancels something, such as a reservation, subscription, or event. The airline's automatic canceller system notified passengers of the flight cancellation.
A device or mechanism that nullifies or negates something, such as noise or a signal. The noise canceller in the headphones made the flight much more enjoyable.
(Philately) A postmark, imprint, or the device used to deface a postage stamp so that it cannot be reused. The rare cover showed a distinctive Maltese Cross canceller applied over the Victorian penny red.