Where does “infernālis” come from?

infernālis (Latin) comes from Latin inferna, from Latin īnfernus.

Ancestry of “infernālis”, step by step

Step	Language	Word	Meaning
1	Latin	inferna	the lower parts of the body, the abdomen;...
2	Latin	īnfernus	—

infernālis — Etymology, Origin & Word History | Etymology Explorer