WordNet: “an on-line lexical reference system whose design is inspired by current psycholinguistic theories of human lexical
memory. English nouns, verbs, adjectives and adverbs are organized into synonym sets, each representing one underlying
lexical concept. Different relations link the synonym sets.

WordNet was developed by the Cognitive Science Laboratory at Princeton University under the direction of Professor George
A. Miller (Principal Investigator).” You can use WordNet online or download your own copy.