Entire means whole and complete, with nothing missing or left out. When you eat an entire pizza by yourself, you've finished every last slice. When you read an entire book in one day, you've gone from the first page to the very last without skipping anything.

The word emphasizes completeness. Your entire class means every single student, not just most of them. If a teacher says to clean your entire desk, she means the whole surface, including those corners where eraser shavings always hide. When someone has your entire attention, you're focused completely on them, not partially distracted by something else.

Entire conveys absolute completeness, stressing that nothing has been excluded or overlooked. If a chef uses the entire lemon, she's using the juice, the zest, and maybe even the rind for her recipe. The word often appears when people want to emphasize they really mean everything: “I spent my entire allowance on that model rocket kit” makes clear you didn't save even a penny.

You'll also hear entirely, the adverb form, meaning completely or fully: “That's entirely up to you” or “I'm not entirely sure about that answer.”