From Middle English pork, porc, via Anglo-Norman, from Old French porc (“swine, hog, pig; pork”), from Latin porcus (“domestic hog, pig”).
Cognate with Old English fearh (“piglet”). Doublet of farrow. Compare also other West Germanic words for pigs: Ferkel, Ferke, and varken.
Used in English since the 14th century, and as a term of abuse since the 17th century.
US politics sense is related to pork barrel.