mainepernour 17th cent variant of 'mainpernor
', surety for a prisoner's court appearance (OED)
(10) Marlowe would have been summarily arrested and required to stay in the Marshalsea prison if he could not find bail, that is, two people prepared to act not only as mainpernors
or sureties for his appearance in court, but also as guarantors liable for the plaintiff's debts and costs should the defendant lose the case and fail to satisfy any judgment against him.
When a loan was negotiated, the borrower had to find mainpernors
, or pledges, who would stand as surety against payment.