That which joins two things so they can reach each other. A connector holds no content of its own.
Latin connectere (to bind together), from com- (together) + nectere (to tie); the agent noun for that which joins two things so each can reach the other.
Its Latin root is tying, and a connector is only ever the tie, never either of the things tied. Its whole purpose disappears the moment the two sides no longer need it.