Haha, I was thinking more like "main potato" ... the main potato in my life is a yam. Uwe na lingoti!
First, is a "yam" the same as a "sweet potato?" If so, I've never heard anyone in TZ say "viazi vikuu" but have heard many times "viazi vitamu." If not, where do they grow yams in TZ?? ha
Not the same thing (usually). Yams can refer to several different plants - arrowroot commonly being one of them. It's a starchy thing eaten similarly to potatoes or cassava.