vital

adj.

[1]	critical , imperative , essential , necessary , needed , requisite , required , indispensable , mandatory , compulsory , cardinal , fundamental , basic , critical , crucial , central , pivotal
[2]	important , life-sustaining , key , central , critical , crucial , life-and-death/life-or-death , pivotal , paramount , main
[3]	lively , full of life , lively , full of life , vivacious , spirited , vigorous , dynamic , alive , animated , brisk , energetic
[4]	invigorating , quickening , life-giving , animating , vitalizing , reviving , vivifying , enlivening , rejuvenating