Overrun/ˈəʊvərʌn/ Definition 1 of 5Pro Tip 1/2Rapid Expansion Use 'overrun' to describe a quick and often unwelcome spread of something. After the storm, the town was overrun by ants. Pro Tip 2/2Negative Connotation 'Overrun' implies a negative impact of being overwhelmed by something. The holiday resort is overrun with tourists during peak season.