From WordNet documentation (http://wordnet.princeton.edu/man/wngloss.7WN): Information in WordNet is organized around logical groupings called synsets. Each synset consists of a list of synonymous words or collocations (eg. 'fountain pen' , 'take in' ), and pointers that describe the relations between this synset and other synsets. A word or collocation may appear in more than one synset, and in more than one part of speech. The words in a synset are logically grouped such that they are interchangeable in some context. Two kinds of relations are represented by pointers: lexical and semantic. Lexical relations hold between word forms; semantic relations hold between word meanings. These relations include (but are not limited to) hypernymy/hyponymy, antonymy, entailment, and meronymy/holonymy. Nouns and verbs are organized into hierarchies based on the hypernymy/hyponymy relation between synsets. Additional pointers are be used to indicate other relations. Adjectives are arranged in clusters containing head synsets and satellite synsets. Each cluster is organized around antonymous pairs (and occasionally antonymous triplets). The antonymous pairs (or triplets) are indicated in the head synsets of a cluster. Most head synsets have one or more satellite synsets, each of which represents a concept that is similar in meaning to the concept represented by the head synset. One way to think of the adjective cluster organization is to visualize a wheel, with a head synset as the hub and satellite synsets as the spokes. Two or more wheels are logically connected via antonymy, which can be thought of as an axle between the wheels. Pertainyms are relational adjectives and do not follow the structure just described. Pertainyms do not have antonyms; the synset for a pertainym most often contains only one word or collocation and a lexical pointer to the noun that the adjective is 'of or pertaining to'. Participial adjectives have lexical pointers to the verbs that they are derived from. Adverbs are often derived from adjectives, and sometimes have antonyms; therefore the synset for an adverb usually contains a lexical pointer to the adjective from which it is derived.