Source : Webster's Revised Unabridged Dictionary (1913)

Mudsill \Mud"sill`\, n.
   The lowest sill of a structure, usually embedded in the soil;
   the lowest timber of a house; also, that sill or timber of a
   bridge which is laid at the bottom of the water. See {Sill}.

Mudsill \Mud"sill`\, n.
   Fig.: A person of the lowest stratum of society; -- a term of
   opprobrium or contempt. [Southern U. S.]