Lewis & Short

commissōrĭus, a, um, adj. [committo]; Lex, in jurid. lang., a clause in the condition of a sale or of a contract (by which a vendor reserved to himself the privilege of rescinding the sale if the purchaser did not pay his purchase-money at the time agreed on), Dig. 18, 3, 14.
So also absol.: com-missōrĭa, ae, f., Dig. 18, 3, 14; 43, 23, 11.