Italian word insieme comes from Latin insimul (Simultaneously. Together.), Latin semel (Once, a single time.), Vulgar Latin *insemel
insimul (Latin)
Simultaneously. Together.
semel (Latin)
Once, a single time.
*insemel (Vulgar Latin)
insieme (Italian)
With, together with, along with (mathematics) set. Whole, ensemble, group At the same time. Together.