One who makes a tick mark.
A measuring or reporting device, particularly one which makes a ticking sound as the measured events occur.
The ticker was showing an increased rate of flow.
A ticker tape, either the traditional paper kind or a scrolling message on a screen.
I checked the prices on the ticker one last time before placing the trade.
A heart, especially a human one.
My ticker gave out and I had to go to the hospital for surgery.
A birdwatcher who aims to see (and tick off on a list) as many bird species as possible.