In "Two Years Before the Mast" Dana describes a visit to
Juan Fernandes, the island where Robinson Crusoe was marooned. He discribes the very attractive fruits and vegegables raised by by the convict the Chlean government
had put there. Among other things he mentions "ground apples". I could not imagine what he meant - until I rembered that he had used a couple words of French origin.
Do you remember the French word for a nutritious fist sized
vegetable dug out of the ground? I'm still surprised that
Dana did not use our word for them.

as in "pomme de terre"?

Vous avez raison, m'sieu.
But doesn't it surprise you a bit to see an American from
Cambridge calling them that. I wonder when current name became preferred.