Synonyms and related words :
balance, bonus, dividend, excess, extra, gratuity, lagniappe, leftover, margin, overabundance, overage, overflow, overkill, overmeasure, overmuch, overrun, overset, overstock, oversupply, plethora, plus, pourboire, redundancy, remainder, something extra, spare, superfluity, surfeit, surplus, surplusage, tip