[v. uhn-der-lahyn, uhn-der-lahyn; n. uhn-der-lahyn]
An underline, also called an underscore, is one or more horizontal lines immediately below a portion of writing. Single, and occasionally double ("double-underscore"), underlining was originally used in hand-written or typewritten documents to emphasise text. In a manuscript to be typeset, various forms of underlining were conventionally used to indicate that text should be set in a special typeface such as italics to show emphasis, part of a procedure known as markup. With the advent of word processing, different typefaces can be used in the manuscript directly, so that underlining is no longer needed for markup; but underlining is sometimes used in documents in its own right.

Underlines are sometimes used as a diacritic, to indicate that a letter has a different pronunciation to its non-underlined form.

Use with computers

In web browsers, default settings typically distinguish hyperlinks by underlining them (and usually changing their color), but both users and websites can change these settings to make some or all hyperlinks appear differently (or even without distinction from normal text).

The HTML special inline element , denoting inserted text, is often presented as underlined text. HTML also has a presentational element , denoting underlined text; this is deprecated in favour of the CSS style {text-decoration: underline}. These elements may also exist in other markup languages, such as MediaWiki.

In plain-text (ASCII) computer files, including e-mail communication, where underlining is not possible, it is often indicated by surrounding words with underscore characters. For example, "You must use an _emulsion_ paint on the ceiling".

Unicode has the combining diacritic "combining low line" at U+0332  ̲ that results in an underline when run together: u̲n̲d̲e̲r̲l̲i̲n̲e̲. Not to be confused is the combining macron below.

Underline (typically red and/or wavy) is often used by spell checkers (and grammar checkers) to denote misspelled or otherwise incorrect text.

Underlines in non-Latin scripts

In Chinese, the underline is a punctuation mark for proper names (專名號, 专名号; pinyin: zhuānmínghào; literally “proper name mark”, used for personal and geographic names). Its meaning is somewhat akin to capitalization in English and should never be used for emphasis; however, due to the influence of English computing, the underline is now sometimes used for emphasis. A wavy underline (書名號, 书名号; pinyin: shūmínghào; literally “book title mark”) serves a similar function, but marks names of literary works instead of proper names.

In the case of two or more adjacent proper names, each individual proper name is separately underlined, so there should be a slight gap between the underlining of each proper name.


The following kinds of underlines are used on manuscripts to indicate special typefaces to be used.


See also

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