Noun
propfan (plural propfans)
(aviation) A modified turbofan jet engine with the propeller outside the engine duct of an aircraft.
However, propfan engines, which are very similar to turboprop engines, can cruise at flight speeds approaching Mach 0.75. Source: Internet
The primary difference between turboprop and propfan design is that the propeller blades on a propfan are highly swept to allow them to operate at speeds around Mach 0.8, which is competitive with modern commercial turbofans. Source: Internet