Which thesaurus (online or paper) best describes the differences between several similar words? As a non-native English speaker, it is often difficult for me to distinguish the slightly different concepts in similar words. I'm looking for a good online dictionary or thesaurus that compares those synonyms word by word.
I use the Oxford American Writer's Thesaurus.
But well, many online dictionaries provide synonymous terms, even if they are not specifically Thesaurus.
For example, the Oxford Advanced Learner's Dictionary sometimes provides synonyms for the terms you search. In such cases it shows the differences in meaning and, above all, in usage. But this is not always the case, unfortunately.
I found a good reference here. You can simply use Google by the way.
WordNet is very good indeed for this, and other kinds of questions like this, because it was constructed specifically for that purpose. In their own words:
WordNet superficially resembles a thesaurus, in that it groups words together based on their meanings. However, there are some important distinctions. First, WordNet interlinks not just word forms—strings of letters—but specific senses of words. As a result, words that are found in close proximity to one another in the network are semantically disambiguated.
Using Thesaurus.com for me has the most advantages. It gives approximately 20 synonyms every time I search for a word. And because it's on the internet and free, it is easily accessible, all the time.