Eng. law, contracts. A species of security which partakes of the nature of a mortgage, as there is a debt due, and an estate is given as a security for the repayment, but differs from it in the circumstances that the rents and profits are to be received without account till the principal money is paid off, and there is no remedy to enforce payment, while the mortgagor has a perpetual power of redemption. 2. It is a species of vivum vadium. Strictly, however, there is this distinction between a Welch mortgage and a vivum vadium. In the latter the rents and profits of the estate are applied to the discharge of the principal, after paying the interest; while in the former the rents and profits are received in satisfaction of his interest only.