Contractûra, contractúræ, f. g. pen. prod. Contracturas in scapis columnarum vocat Virtuuius, qua gracilescunt. The making small of pillars toward the toppe.
Lewis and Short: Latin dictionary
contractūra, ae, f. [id.; lit. a drawing together; hence], t. t. in architecture, a lessening, contracting (of pillars), Vitr. 3, 3, 12; 5, 1, 3 al.