The Collaborative International Dictionary
Bridgeboard
Bridgeboard \Bridge"board`\, n.
(Arch.) A notched board to which the treads and risers of the steps of wooden stairs are fastened.
A board or plank used as a bridge.
Wiktionary
bridgeboard
n. 1 (context architecture English) A notched board to which the treads and risers of the steps of wooden stairs are fastened. 2 A board or plank used as a bridge.