gargantuan
Extremely, unbelievably large in size or amount.
Gargantuan means incredibly, unbelievably huge. A gargantuan sandwich towers so high you can barely fit it in your mouth. A gargantuan homework assignment might take hours to complete. A gargantuan elephant could weigh over six tons.
Today, we use gargantuan when ordinary words like “big” or “large” just aren't enough to capture the scale of something.
You might describe a gargantuan building that stretches fifty stories into the sky, or the gargantuan task of organizing thousands of books in a library. Notice how the word emphasizes size and the feeling of being overwhelmed by that size. A gargantuan problem feels almost impossibly large, difficult in a way that makes you wonder how you'll ever solve it. A gargantuan amount of ice cream is a mountain of dessert that could feed a whole party.
The word works for physical size, but also for abstract ideas: a gargantuan effort, a gargantuan success, or gargantuan courage.