modus

noun3

1. •
   A qualification involving the idea of variation or departure from some general rule or form, in the way of either restriction or enlargement, according to the circumstances of the case, as in the will of a donor, an agreement between parties, etc.
2. •
   A fixed compensation or equivalent given instead of payment of tithes in kind, expressed in full by the phrase modus decimandi.

   • To make a good and sufficient modus, the following rules must be observed — 1765
3. •
   (no longer used) The arrangement of, or mode of expressing, the terms of a contract or conveyance.