"Key the city" can be defined as a term that refers to the act of locking down a city or a particular area through strict security measures. There are several synonyms associated with this phrase, including "lockdown," "seal off," and "secure." These terms all imply a sense of control and the imposition of strict measures to prevent unauthorized access. "Key the city" is often used in situations where there is a perceived threat to public safety, whether due to a natural disaster or a criminal incident. By locking down the area, authorities can ensure that people are safe and that order is maintained.