Growing up my Grandfather would ask my Mother to cook some black eyed peas for good luck in the New Year. I'm having trouble remembering the Spanish word that he would use. What could it be?
It will depends on what Spanish region you were living, because for the common food (like the peas), every region can have his own name.
Usually you can translate "Peas" as "Guisantes". But, there are more similar legumes that could be 'Peas'. It's the same with the word "Nuts" that can refer to: Almendras, Nueces, Avellanas, etc...
As I don't know any "Black Guisante" (they are greens), I can suppose that the word was: "Habichuelas"