While there’s no pea in peacock, the kind of green pea that people eat deserves a look in its own right. The singular of that word in Old English was pise, which in Middle English became pease. From its pronunciation, that eventually got taken for a plural, so English speakers created the new and unambiguous singular pea. According to the American Heritage Dictionary, the word originally came into Old English from Late Latin pīsa, which was a variant of the pīsum that Latin had taken from Greek pisos, pison.
Although the most common Spanish word for ‘pea’ is probably the unrelated arveja, pea does have two roughly synonymous relatives in Spanish. The one that’s not hard to recognize is pésol. It came into Spanish from Catalan pèsol, which had developed from pīsulum, a diminutive of Latin pīsum. And then there’s guisante, which almost no one would suspect is an etymological relative. It owes its disguise to the fact that it entered Spanish from Arabic. The Arabs had most likely borrowed the Latin phrase pīsum sapidum, in which the adjective, which Spanish has borrowed as sápido, meant ‘tasty.’ That phrase was phonetically reduced on its way to becoming Mozárabe biššáuṭ, which then passed into various Spanish dialects. The modern form guisante is due to influence from the unrelated verb guisar ‘to stew, to cook.’
© 2016 Steven Schwartzman