Rootsy is a word people use about music. Rootsy music is played in the older, more traditional way for that style — closer to folk, blues, country, or reggae as they sounded before they became glossy pop. You might hear a reviewer say a band is rootsy if the guitars are raw, the songs feel homemade, and you can still hear the roots of the style. It is informal, almost a fan or magazine word, not a word for a test paper. Though actually, it is not about plant roots, and it is not a spelling of rusty. It praises a kind of honesty in the sound, not a kind of dirt.