If something is essential, it’s important. Use this adjective to describe things that are necessary to have. You can pronounce this word in one of two ways: essential (long e) or essential (schwa sound).
Participation in class is essential to your success as a student.
Kevin is an essential member of our team. Without him, we wouldn’t do as well.
Fruits and vegetables are essential to a person’s diet.
All nonessential staff were excused from work today because of the power failure. (To make the negative form of the word, add "non.")
Learning English is an essential part of your education.
The adverb form of this word is "essentially." When used as an adverb, the meaning is similar to other adverbs, "fundamentally" and "basically."
These two ideas are essentially the same.
The software we need to complete our project is essentially free.