essential

absolutely necessary; vitally necessary

• “essential tools and materials”
• “funds essential to the completion of the project”
• “an indispensable worker”

basic and fundamental

• “the essential feature”

of the greatest importance

• “the all-important subject of disarmament”
• “crucial information”
• “in chess cool nerves are of the essence”

being or relating to or containing the essence of a plant etc

• “essential oil”

applying to essential legal principles and rules of right

• “substantive law”

absolutely required and not to be used up or sacrificed

anything indispensable

• “food and shelter are necessities of life”
• “the essentials of the good life”
• “allow farmers to buy their requirements under favorable conditions”
• “a place where the requisites of water fuel and fodder can be obtained”