A general rule is that you should not use a thesaurus to substitute words in your GRE essay. Although you won't have access to a thesaurus when you take the GRE test, refrain from using grandiose-sounding words in an attempt to make your essay sound much more scholarly than it really is. Often-times, the most powerful ideas are expressed using simple, straight-forward language that is easy to understand and discernible by everybody. And, your score on the GRE essays is partially dependent on how well you use language. The GRE Essay scoring guide, available on the ETS website, lists several criteria that are used to determine GRE essay scores. For high scoring essays, users must express ideas fluently and precisely, using effective vocabulary and sentence variety.

The most common mistake in using a thesaurus or is to choose words that you are not familiar with that may have different meanings that you do not know. Also, you want to select those words that help to convey the exact message that you want to get across. Most commonly words that are not appropriate for your claims or arguments will only confuse your audience and make your essay difficult to understand.

For example, consider the following sentence:

I was very excited to be leaving home on my way to college.

The example sentence is very easy to understand and the meaning is straight forward. However, if you were to use words that you are not quite familiar with, in an attempt to make the sentence sound more complicated than it really is, then you might have written:

I was very animated to be departing home on my way to college.

Here only two words are changed, but suddenly it is difficult to understand the intended meaning of the sentence. The word "animated," while it is a synonym for excited, does not exactly fit the sentence and "departing" carries connotations with it that “leaving” does not.