Etymology
Named for its width, which is equal to the width of the letter m or M, or approximately twice the width of an en dash.
Noun
em dash (plural em dashes)
- (typography) The symbol (—) (used to demarcate a parenthetical thought or to indicate a break, or for emphasis)
Usage notes
In recent usage, some style guides (especially in the UK and Canada) have proscribed the parenthetical em dash (—), instead mandating the use of a spaced en dash (–),[1][2] though this is not universally accepted.[3] For example:
- The room – dark and depressing – was at the end of the corridor.
Rather than:
- The room—dark and depressing—was at the end of the corridor.
These symbols are often identical in appearance and can be used as quotation dashes:
- — (em dash)
- ― (horizontal bar)
References
“m-dash (—)”, in University of Oxford Style Guide, Oxford University Press, 2014, page 13: “m-dash (—) - Do not use; use an n-dash instead.”
“Hyphens, En Rules and Em Rules”, in Editorial Services Style Guide for Academic Books, Cambridge University Press, 2023, page 12: “Spaced en rules (or ‘en dashes’) must be used for parenthetical dashes. Hyphens or em rules (‘em dashes’) will not be accepted for either UK or US style books. En rules (–) are longer than hyphens (-) but shorter than em rules (—).”
“Dashes”, in Google developer documentation style guide, Google, 2024:Don't use an en dash (the shorter dash) or a hyphen in place of an em dash. The use of an en dash with spaces around it in place of an em dash is gradually becoming more common, but it's still not very widespread in the US in professional publishing; so far (as of early 2016), it's mostly used in Canada and a few other places. For now, only use the em dash.