The Collaborative International Dictionary of English v.0.48:

Frank-law \Frank"-law`\, n. [Frank free + law.] (Eng. Law)
   The liberty of being sworn in courts, as a juror or witness;
   one of the ancient privileges of a freeman; free and common
   law; -- an obsolete expression signifying substantially the
   same as the American expression civil rights. --Abbot.
   [1913 Webster]