To increase means to become larger, greater, or more numerous. When a plant increases in height, it grows taller. When the temperature increases, it gets warmer. When a company increases its prices, things cost more than they did before.

The word works as both a verb and a noun. You can increase your vocabulary by reading more books (verb), or you can notice an increase in your vocabulary over time (noun). A baker might increase the amount of sugar in a recipe, or a runner might track the increase in her speed after months of practice.

Increase is the opposite of decrease. If your allowance increases from five dollars to seven dollars, you're getting more money. If it decreases from seven dollars back to five, you're getting less.

The word often appears in discussions about numbers, measurements, and quantities. Scientists measure the increase in ocean temperatures. Teachers notice when students show an increase in confidence. Coaches celebrate increases in team performance. Whenever something grows larger, stronger, faster, or more abundant, it increases. The key idea is simple: you end up with more than you started with.