Define That Term #12

Yesterday's term was inchoate, which is defined as:

adj. or adv. referring to something which has begun but has not been completed, either an activity or some object which is incomplete. It may define a potential crime like a conspiracy which has been started but not perfected or finished (buying the explosives, but not yet blowing up the bank safe), a right contingent on an event (receiving property if one outlives the grantor of the property) or a decision or idea which has been only partially considered, such as a contract which has not been formalized.

Slickdpdx got it right, but Richard gets bonus points for creativity!

Today's term is:

pro tanto.