Serious/ˈsɪriəs/ Definition 1 of 5Pro Tip 1/3Severity Indicator Use 'serious' for situations that are potentially dangerous or require immediate attention. After the accident, he was in a serious condition. Pro Tip 2/3Not Trivial 'Serious' suggests an issue is not to be taken lightly and may have significant outcomes. Ignoring climate change can have serious implications. Pro Tip 3/3Considerable Importance About issues demanding careful consideration or considerable resources. She has a serious decision to make about her career.