from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
MAINPERNORS, English law. Those persons to whom a man, is delivered out of
custody or prison, on their becoming bound for his appearance.
2. Mainpernors differ from bail: a man's bail may imprison or surrender
him up before the stipulated day of appearance; mainpernors can do neither,
but are merely sureties for his appearance at the day; bail are only
sureties that the party be answerable for all the special matter for which
they stipulate; mainpernors are bound to produce him to answer all charges
whatsoever. 3. Bl. Com. 128; vide Dane's Index, h.t.