Definitions of infernal:

• noun:   an inhabitant of hell

  Example: "His roar made the infernals quake"

• adjective:   being of a lower world of the dead

  Example: "Infernal regions"

• adjective:   characteristic of or resembling hell

  Example: "Infernal heat and noise"

• adjective:   relating to or inhabiting hell

  Example: "His infernal majesty"

• adjective:   expletives used informally as intensifiers

  Example: "An infernal nuisance"

• adjective:   extremely evil or cruel; expressive of cruelty or befitting hell

  Example: "Infernal instruments of war"