basic 普通用词，指明确、具体的基础或起点。
essential 语气比basic和fundamental强，强调必不可少，暗含某物如缺少某部分，则失去本质特征的意味。
fundamental 书面用词，不如basic使用广泛，侧重指作为基础、根本的抽象的事物。
radical 着重指事物的根本或其来源。
vital 正式用词，侧重指维持生命、活力必不可少的，或生死攸关的。
参考例句
1. It was a radical experiment. 这是一个基本的实验。
2. They wish to adopt more radical methods. 他们希望采取更激烈的方法。
3. One obvious impact is the radical alteration of the land surface. 一种显而易见的影响是大地表面剧烈的改变。
英英解释
n.
1. (chemistry) two or more atoms bound together as a single unit and forming part of a molecule
2. an atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygen m
3. a person who has radical ideas or opinions
4. a character conveying the lexical meaning of a logogram
5. a sign placed in front of an expression to denote that a root is to be extracted
6. (linguistics) the form of a word after all affixes are removed adj.
1. (used of opinions and actions) far beyond the norm
2. markedly new or introducing radical change
3. arising from or going to the root
4. of or relating to or constituting a linguistic root
5. especially of leaves; located at the base of a plant or stem; especially arising directly from the r
