Dictionary.net

• A board on the fore part of a vehicle to prevent water or mud from being thrown upon those in it by the heels of the horses.

1914 - Nuttall's Standard dictionary of the English language
By Nuttall, P.Austin.

• A board on the fore part of a vehicle to prevent water, mud, or snow being thrown upon the persons in it by the heels of the horses.

1874 - Etymological and pronouncing dictionary of the English language
By Stormonth, James, Phelp, P. H.