Plus  —prep. 1  with the addition of (symbol +). 2 (of temperature) above zero (plus 2°). 3 colloq. With; having gained; newly possessing. —adj. 1 (after a number) at least (fifteen plus). 2 (after a grade etc.) Rather better than (beta plus). 3 math. Positive. 4 having a positive electrical charge. 5 (attrib.) Additional, extra. —n. 1 the symbol +.