"Cover" doesn't work with traditional music. Who are you "covering" when you don't know the author? Some songwriters, such as Woody Guthrie, have written songs that so many people sing, that the gap between "traditional" and "singer-songwriter" is perilously thin. I'm OK with calling it a "cover" if the person didn't write it, and the song is somewhat well-known.

But then, you have Joni covering that Judy Collins song "Clouds", and Warren Zevon covering Linda Ronstadt's "Poor, Poor, Pitiful Me". It's just another word to get misused and misunderstood.