red-letter \ˈ ̷ ̷| ̷ ̷ ̷ ̷\adjective 1.: employing red letters to call attention to something of special significance < red-letter Bible > 2.[so called from the practice of marking holy days in red letters in church calendars]: of special significance : happy, memorable < red-letter day > < the testimonial dinner was a red-letter occasion >