red thread or string; a line drawn in red color; (figurative) a bottom line or warning line that must not be crossed, such as in law or safety regulations
marriage tie
the invisible thread that binds two people destined for marriage; matchmaking
boundary
a boundary line for urban construction and road use in architectural drawings
central theme
a core idea or main thread that runs through a piece of writing or a creative work
Hong Xian
a female character in the Tang dynasty legend of the same name, a maid of the military governor Xue Song
