absolutely required and not to be used up or sacrificed
absolutely necessary; vitally necessary; "essential tools and materials"; "funds essential to the completion of the project"; "an indispensable worker"
being or relating to or containing the essence of a plant etc; "essential oil"
manifesting or characteristic of life; "a vital, living organism"; "vital signs"
performing an essential function in the living body; "vital organs"; "blood and other vital fluids"; "the loss of vital heat in shock"; "a vital spot"; "life-giving love and praise"