reserve

¹re·serve

noun \ri-ˈzərv\

Definition of RESERVE

1

: something stored or kept available for future use or need <oxygen reserve>—see cardiac reserve

2

: the capacity of a solution to neutralize alkali or acid when its reaction is shifted from one hydrogen-ion concentration to another; especially : the capacity of blood or bacteriological media to react with acid or alkali within predetermined and usually physiological limits of hydrogen-ion concentration—compare buffer, buffer solution