La·pis n.; pl. Lapides   A stone.
 Lapis calaminaris n. [NL.] Min. Calamine.
 Lapis infernalis n. [L.] Fused nitrate of silver; lunar caustic.
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 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.