Links to some useful documentation
A wordnet is semantic network. Synonymous words (including MWEs) are grouped into synsets. These synsets are then linked to other synsets via semantic relations such as hypernym. Ideally, the meaning of a synset is further clarified with a short defining definition (or gloss) and or more usage examples.
Originally, Princeton WordNet only included the lexical categories of major content words: nouns, verbs, adjectives and adverbs. Other wordnets have added other parts of speech, such as pronouns and exclamatives.
Source code hosted at https://github.com/omwn/omwn.github.io.