Sounds like jicama to me.

I have been searching for a paleo substitute for potatoes and tried
parsnips, rutabagas and jicama. Parsnips were OK, as were rutabagas,
but a
bit strong tasting. I use sweet potatoes occaisionally. Jicama tastes
great, but, as you discovered, never softens - it always stays
crunchy. It
does taste great, though, and can be diced into anything that need a
crunch
and a light sweetish fresh flavor. Cooking doesn't seem to change it
at
all, so I eat it raw.
Now I will try celeriac, when I can find it.

>../he thought it
>might be jicama. I did end up buying one, boiling it and
>eating it, but it didn't taste/look like it. It was a lot
>more hard, and crunchy, and I did boil it for at least
>an hour. Does anyone know what this veggie was, or if maybe
>it was jicama, but I bought one that wasn't ripe or something?
>Thanks,
>--Liz
>>
>>jicama (hee-ca-ma) is another potato substitute, great in stews.