To rethink something means to think about it again, often in a new way that leads you to change your mind or approach. When you rethink a decision, you reconsider whether it was the right choice. When you rethink a plan, you look at it fresh and might spot better ways to do it.

Rethinking happens when new information appears or when your first attempt doesn't work out. Maybe someone planned to organize a science project one way, but after starting, they realize they need to rethink their approach. A soccer coach might rethink her strategy at halftime if the other team is playing differently than expected.

The word means genuinely thinking something through again with care and attention, with a purpose behind the reconsideration. Scientists rethink their theories when new evidence emerges. Writers rethink their stories when the plot isn't working. Sometimes it's wise to pause and rethink your direction rather than stubbornly sticking with a plan that isn't working.