red line

noun

1. Ice Hockey.,  a line of the color red that is parallel to and equidistant from the goal lines and divides the rink in half.

2. a limit, point, or boundary beyond which one may not go without incurring negative consequences.

   The use of chemical weapons is a red line, which, if crossed, could trigger military action.

red line

noun

1. a point beyond which a person or group is not prepared to negotiate

Word History and Origins

Origin of red line¹

First recorded in 1960–65