What does "plim" mean?

Plim: To swell, as grain or wood with water. [Prov. Eng.] Grose. PLIMSOLL'S MARK Plim"soll's mark`. (Naut.) A mark conspicuously painted on the port side of all British sea-going merchant vessels, to indicate the limit of submergence allowed by law; -- so called from Samuel Plimsoll, by whose efforts the act of Parliament to prevent overloading was procured.