mar vs underline

mar

• To spoil; to ruin; to scathe; to damage. 

• A small lake. 

• A blemish. 

underline

• To emphasise or stress something 

• To draw a line underneath something, especially to add emphasis; to underscore 

• A line placed underneath a piece of text in order to provide emphasis or to indicate that it should be viewed in italics or (in electronic documents) that it acts as a hyperlink. 

• The character _. 

• Passing under a railway line.