noun

• One who makes a tick mark.
• A measuring or reporting device, particularly one which makes a ticking sound as the measured events occur.
• A ticker tape, either the traditional paper kind or a scrolling message on a screen.
• (slang) A heart, especially a human one.
• (slang) A watch (timepiece).
• (birdwatching, slang) A birdwatcher who aims to see (and tick off on a list) as many bird species as possible.