The word hundredweight derives from its definition as close to $100$ pounds avoirdupois.
Its plural form is hundredweight, not hundredweights.
The word avoirdupois derives from the Norman French word whose literal translation is goods (that is property, or things owned) of weight.
The avoir part also means to have in modern French, and derives from the Latin habere.
It is pronounced something like av-wah-doo-pwah, although Francophones will be aware that there are further subtleties to this.