Intentionally means doing something on purpose, not by accident. When you intentionally leave your homework at home, you meant to do it. When you trip over your shoelaces, that's an accident, but when you intentionally tie someone else's shoelaces together as a prank, you planned it.

If you intentionally practice piano every day, you're choosing to do it as part of a goal. If you accidentally knock over a glass of milk, nobody can say you did it intentionally because you had no plan to spill it.

Understanding intention matters when figuring out whether someone should face consequences. Breaking a friend's toy accidentally is very different from breaking it intentionally. Teachers, parents, and judges all consider whether someone acted intentionally when deciding how to respond. A student who intentionally copies another student's work faces different consequences than one who accidentally uses similar wording.

The opposite of intentionally is accidentally, unintentionally, or by mistake. When you want to make clear that you did something deliberately and with purpose, intentionally is the perfect word.