Noun
pondus
(historical) An old English measure of weight, usually of wool, perhaps equal to 3 cloves.
Another suggestion is that the "p" stands for the Latin terms pondus hydrogenii (engl. quantity of hydrogen), potentia hydrogenii (engl. capacity of hydrogen), or potential hydrogen. Source: Internet
Weight was split into a "still weight" or pondus, which remained constant, and the actual gravity or gravitas, which changed as the object fell. Source: Internet