salto mortale

plural salti mortali

1. A dangerous and daring jump with possibly lethal outcome.
2. figurativelyA risky, dangerous or crucial step or undertaking.

   The frenzied, suggestible, gregarious, subconscious self, freed from all rational restraints, celebrated its delirious orgies, its corybantic bacchanalia, held its mad salto mortale over the grave of crucified humanity.

   1919, Boris Sidis, The Source and Aim of Human Progress

   1 more example

   I take shame to myself…for having been more taken by the salti mortali* of a waiter who summed up my account at a Paduan restaurant, than by all the strategies with which the city has been many times captured and recaptured. * Salti mortali are those prodigious efforts of mental arithmetic by which Italian waiters, in verbally presenting your account, arrive at six as the product of two and two.

   1867 July, William Dean Howells, “At Padua”, in The Atlantic Monthly: A Magazine of Literature, Science, Art, and Politics, volume XX, № CXVII, chapter i, page 25/1