Acheronian and All-fired

Acheronian adjective - Dark and dismal as of the rivers Acheron and Styx in Hades.

All-fired and acheronian are semantically related. In some cases you can use "All-fired" instead an adjective "Acheronian".

All-fired adjective - Extreme; used as an intensifier.

Acheronian and all-fired are semantically related. Sometimes you can use "Acheronian" instead an adjective phrase "All-fired".