underline

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 _.

(old-fashioned) A caption beneath a photograph (which may have more than one line of text).

(old-fashioned) An announcement of a theatrical performance to follow, placed in an advertisement for the current one.

To draw a line underneath something, especially to add emphasis.

(figurative) To emphasise or stress something.

(figurative, no longer used) To influence secretly.

Passing under a railway line.