In·fer·nal a.
1. Of or pertaining to or suitable for the lower regions, inhabited, according to the ancients, by the dead; pertaining to Pluto's realm of the dead, the Tartarus of the ancients.
The Elysian fields, the infernal monarchy. --Garth.
2. Of or pertaining to, resembling, or inhabiting, hell; suitable for hell, or to the character of the inhabitants of hell; hellish; diabolical; as, infernal spirits, or conduct.
The instruments or abettors in such infernal dealings. --Addison.
Infernal machine, a machine or apparatus maliciously designed to explode, and destroy life or property.
Infernal stone (lapis infernalis), lunar caustic; formerly so called. The name was also applied to caustic potash.
Syn: -- Tartarean; Stygian; hellish; devilish; diabolical; satanic; fiendish; malicious.