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"
the heavy fire of artillery to saturate an area rather than hit a specific target; "they laid down a barrage in front of the advancing troops"; "the shelling went on for hours without pausing"
the rapid and continuous delivery of linguistic communication (spoken or written); "a barrage of questions"; "a bombardment of mail complaining about his mistake"