The address book of living lines — where every lamp's number is kept and any voice can be reached.
A compound of switch, itself probably Middle Dutch or Low German swijch (a flexible twig, a bough), and board, Old English bord (a plank, a flat surface); a telephone-exchange word for the panel where any line could be connected to any other.
The address book of living lines, where every lamp's number is kept and any voice can be reached. Named for the literal panel where a call was once switched by hand.