thinking again about a choice previously made
"he had second thoughts about his purchase"
The act of thinking again about something.
"After reading the new data, we need to rethink our strategy for launching the product next month."
To think again about a problem.
"After noticing the budget was running low, we decided to rethink how we were spending our money on marketing."
This word comes from combining the prefix re- with think. It originally meant to think again or consider something anew.