1. past tense and past participle of underscore; emphasized or highlighted the importance of something
2. past tense and past participle of underscore; drew a line under text

Examples

• The teacher underscored the importance of studying for the exam.
• His speech underscored the need for immediate action on climate change.
• The recent events have underscored our vulnerability to cyber attacks.
• She underscored key phrases in the document with a red pen.
• The statistics underscored the growing inequality in the region.
• The accident underscored the dangers of texting while driving.
• He underscored his signature on the contract.