Thayer's Greek Lexicon

 1. a touchstone, which is a black siliceous stone used to
test the purity of gold or silver by the colour of the
streak produced on it by rubbing it with either metal
2. the rack or instrument of torture by which one is forced
to divulge the truth
3. torture, torment, acute pains
  1) of the pains of a disease
  2) of those in hell after death