Frequency: The word is one of the 3000 most common words in English.
1.
You use ~ to describe things, activities, and principles that are very important or essential. They affect the basic nature of other things or are the most important element upon which other things depend.
Our constitution embodies all the ~ principles of democracy...
A ~ human right is being withheld from these people...
= basic
ADJ: usu ADJ n
2.
You use ~ to describe something which exists at a deep and basic level, and is therefore likely to continue.
But on this question, the two leaders have very ~ differences...
= profound
ADJ: usu ADJ n
3.
If one thing is ~ to another, it is absolutely necessary to it, and the second thing cannot exist, succeed, or be imagined without it.
The method they pioneered remains ~ to research into the behaviour of nerve cells.
= vital
ADJ: v-link ADJ to n
4.
You can use ~ to show that you are referring to what you consider to be the most important aspect of a situation, and that you are not concerned with less important details.
The ~ problem lies in their inability to distinguish between reality and invention...
= basic
ADJ: ADJ n