ultra-fast

From ultra- +‎ fast.

ultra-fast (not comparable)

1. Alternative form of ultrafast
   • 1960 February, “Talking of Trains”, in Trains Illustrated, page 67:

     Less important lines of plain double track carrying a mixture of passenger and freight traffic cannot be given ultra-fast expresses, and where alternative routes exist, as for example between London and the West Riding, the specially high-speed trains must be restricted to one of them only.

• “ultra-fast”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.