Adagissimo: significado y uso en música

¿Cómo se toca adagissimo?

Toca en un tempo extremadamente lento, más fuerte y más lento que un adagio ordinario.

¿Cómo suena adagissimo?

Extreme, weighted slowness — slower and more emphatic than adagio.

I could not find adagissimo in a single major reference dictionary — not Oxford, not Treccani, not even the 1880 Grove. The one real trace is a 1921 American textbook that places it, by name only, among the very slowest tempo words: grave, larghissimo, adagissimo, lentissimo. No number attached, then or since. My guess is the word simply outran its own usefulness — very, very slow was already covered by grave and larghissimo, and adagissimo never quite found its own space.