red line

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red line (plural red lines)

1. (ice hockey) The thick red line on the ice which divides the rink in half.
2. (figuratively) A boundary or limit which should not be crossed.
   • 2013 May 4, Daniel Byman, “Mr. Obama, Don’t Draw That Line”, in The New York Times‎, →ISSN:

     The administration’s ultimatum now seems like cheap talk, and it illustrates the risks of carelessly drawing red lines and issuing highly public threats that won’t be enforced.

• blue line
• goal line (“thin red lines in front of the goals”)
• green line
• redline (verb)
• single yellow line

• “red line”, in Collins English Dictionary.
• “red line”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.
• “red line” in the Cambridge English Dictionary, Cambridge: Cambridge University Press.

• Nile red, relined