The suffix -er gets added to the end of words to create new meanings, most commonly to show “someone who does something” or “something that does something.”

Add -er to a verb and you get a person or thing that performs that action. A teacher teaches. A baker bakes. A player plays. A toaster toasts bread. A computer computes (or did, before we started using them for everything else too).

Sometimes -er creates words describing things rather than people: a scraper scrapes, a heater heats, and an eraser erases pencil marks.

The suffix also appears in comparison words. When you add -er to an adjective, you're comparing two things. If your friend is tall, you might be taller. If a problem is hard, the next one might be harder. If today is cold, tomorrow might be colder. This comparing use of -er pairs with -est for the ultimate degree: tall, taller, tallest.

You'll also see -er showing where someone comes from or what they do professionally. A New Yorker lives in New York. A foreigner comes from a foreign country. A baker bakes bread for a living.

Not every word ending in the letters e-r uses this suffix (like water or butter), but when you spot -er added to a recognizable root word, you're probably looking at someone or something that does whatever that root word describes.