- Lydian stone; basanite; -- so called because used to
test the purity of gold and silver by the streak which is left upon the
stone when it is rubbed by the metal. See Basanite. - Any test or criterion by which the qualities of a thing
are tried.
Meaning of 'touchstone' (Princeton's WordNet)
1 . touchstone
[ n]
Meaning (1): - a basis for comparison; a reference point against which other things can be evaluated