"the seed of a hardy leguminous vine," a well-known article of food, early or mid-17c., a false singular from Middle English pease (plural pesen), which was both single and collective (as wheat, corn) but the "s" sound was mistaken for the plural inflection. From Old English pise (West Saxon), piose (Mercian) "pea," from Late Latin pisa, variant of Latin pisum "pea," probably a loan-word from Greek pison "the pea," a word of unknown origin (Klein suggests it is from Thracian or Phrygian).
In Southern U.S. and the Caribbean, used of other legumes as well. Pea soup "soup made from peas" is recorded by 1711 (as pease-soup); the term was applied to London fogs at least since 1849. Pea-green as a hue resembling fresh peas is by 1752. Pea-shooter "toy consisting of a long straw or tube through which dried peas may be blown" is attested from 1803.