Definitions
1.nounA 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.
2.nounThe character _.
3.nounAn announcement of a theatrical performance to follow, placed in an advertisement for the current one.
4.verbTo draw a line underneath something, especially to add emphasis; to underscore"underline the important words in the text"
5.verbTo emphasise or stress something
6.verbTo influence secretly.
7.adjectivePassing under a railway line.