Noun
(figuratively) Something shared between two or more people, such as an interest, hobby, or experience, that causes their relationship with each other to strengthen.
Used other than figuratively or idiomatically: see tie, bind.
Source: en.wiktionary.orgI keep a close watch on this heart of mine; I keep my eyes wide open all the time. I keep the ends out for the tie that binds. Because you're mine, I walk the line. Johnny Cash
Th' Turkey bur-rd's th' rale cause iv Thanksgivin'. He's th' naytional air. Abolish th' Turkey an' ye desthroy th' tie that binds us as wan people. Finley Peter Dunne
I think things like food, the food of the south is sort of the common tie that binds us all, Black and White, the sense memories. It's a very particular part of the country. Sela Ward
One can be a brother only in something. Where there is no tie that binds men, men are not united but merely lined up. Antoine de Saint Exupéry