Why was the G-sharp to E-flat interval called the wolf in meantone tuning?

In meantone temperament, the interval between G-sharp and E-flat was called the "wolf" because it was severely out of tune, producing a harsh, dissonant sound that was likened to the howling of a wolf.12

This dissonance occurred because meantone tuning was designed to provide pure major thirds by flattening the fifths. Because keyboard instruments had a limited number of keys per octave, they could not accommodate both sharps and their enharmonic flat equivalents (such as G-sharp and A-flat) simultaneously. When a composition required a note outside the system's intended range—such as using G-sharp in a context where E-flat was expected—the resulting enharmonic fifth (G-sharp to E-flat) was nearly two commas out of tune. This interval was significantly more dissonant than the mistuned fifths found in other systems, leading to the "wolf" designation.12