means The sharp, acidic taste sensation — like lemon or vinegar — or, figuratively, a bitter, ill-tempered mood.

from From the Old English "sur," meaning sour or acid, with the "-ness" suffix marking it as a state or quality. The root reaches back to a Proto-Germanic "suraz" (still visible in German "sauer" and the Scandinavian "surt"), and it's likely a distant cousin of words across Indo-European languages clustering around the idea of bitter or salty. So the taste came first; the surly disposition is a later borrowing of the flavor, the tongue lending its vocabulary to the temper.