【Superfluous】 , 【surplus】 ,  【supernumerary】 ,  【extra】 ,  【spare】  all describe what is above or beyond what is needed or indispensable.

【Superfluous】 implies a superabundance or excess that requires elimination or pruning.

Sometimes the term either loses its implication of richness of supply or places no emphasis on that idea and comes to mean little more than nonessential or dispensable , if circumstances require its sacrifice or unnecessary , useless , or needless .

【Surplus】 applies to what remains over when what is needed or required for all present purposes has been used.

【Supernumerary】 implies something added to a number that is normal, adequate, or prescribed; it need not necessarily suggest that there is no need or no use for what is added, though in reference to a physical condition it often implies a departure from the normal.

【Extra】  is often used in place of  【supernumerary】 , but it may also apply to an addition not in number but in amount or in price.

【Spare】  is often used in place of  【surplus】 but it carries a stronger suggestion of being held for future use, often a special use or of not having any demands on it for a particular use or of being easily spared.