Tremendous means extraordinarily large in size, extent, amount, power, or degree. It can also mean really marvelous and fantastic — or really awful and terrible.
We often use tremendous if something is super wonderful. If someone comes into your office and tells you you just won a big contract and are getting a huge bonus, you might exclaim, “Tremendous!” Tremendous comes from the Latin for "trembling," and is connected with fear. Something tremendous can be big in a terrifying way, like the tremendous noise of an approaching hurricane, or a tremendous tidal wave about to crash on the shore.