washboard
washboard is a scraped board.
Also recorded as rubboard.
Overview
Musical percussion instrument.
In detail
It is associated with United States.
Sources
Each source is named with the standing the house places on it, so the evidence can be weighed rather than taken on trust.
reference work · Reputable secondary · Wikipedia
“Washboard (musical instrument)”, English Wikipedia, consulted as further reading
Consult the sourcereference work · Reputable secondary · Wikidata
Wikidata, structured authority record Q21607265: washboard
Consult the source