Did you know?

Click any word in a definition or example to find the entry for that word

red line - definition and synonyms


What are red words?

90% of the time, speakers of English use just 7,500 words in speech and writing. These words appear in red, and are graded with stars. One-star words are frequent, two-star words are more frequent, and three-star words are the most frequent.



The thesaurus of synonyms and related words is fully integrated into the dictionary. Click on the thesaurus category heading under the button in an entry to see the synonyms and related words for that meaning.

noun [countable] red line pronunciation in American English /ˌred ˈlaɪn/
Word Forms
singularred line
pluralred lines
  1. a statement, typically by a government, of acts that they regard as unacceptable and will respond to

    The use of chemical weapons during war is a red line issue.

Word story
Red line has been used since the 1970s to denote a limit beyond which someone must not go without facing severe consequences. It suggests the idea of a physical boundary marking the limits between acceptable and unacceptable behavior, and is related to expressions such as ’cross a line’ and ’draw a line in the sand’.


a title used before a man or woman's name as a gender-neutral alternative to Mr, Ms, etc

BuzzWord Article

Open Dictionary


another way of saying congratulations, or that something/someone looks nice or fascinating

add a word


A must for anyone with an interest in the changing face of language. The Macmillan Dictionary blog explores English as it is spoken around the world today.

global English and language change from our blog
Macmillan learn live love play