clapboard n.

1520s, partial translation of Middle Dutch klapholt (borrowed into English late 14c. as clapholt), from klappen "to fit" + Low German holt "wood, board" (see holt). Compare German Klappholz.

Originally small boards of split oak imported from northern Germany and cut by coopers to make barrel staves; the meaning "long, thin board, usually about 6 or 8 inches wide, used for roofing or to cover the exterior of wooden buildings" is from 1630s, American English.