lexicon.json is a pruned derivative of Open English WordNet.

  Open English WordNet 2024
  https://en-word.net
  Licensed under the Creative Commons Attribution 4.0 International Licence
  (CC BY 4.0): https://creativecommons.org/licenses/by/4.0/

Open English WordNet is itself derived from Princeton WordNet:

  Princeton University "About WordNet." WordNet. Princeton University. 2010.
  https://wordnet.princeton.edu/

CC BY 4.0 permits commercial use and redistribution, including of a modified
version, on the condition that attribution is given and changes are stated. Both
are here.

What was changed, in full:

  * Only noun and verb entries were kept. Adjectives and adverbs were dropped.
  * Only the `derivation` sense relation was kept. Every other relation --
    hypernymy, meronymy, antonymy and the rest -- was dropped.
  * Derivational links were resolved from sense identifiers to written forms,
    lower-cased, and stored symmetrically. WordNet records the relation in one
    direction on some pairs and in both on others; a one-sided link would make a
    match depend on which word a user happened to type.
  * Verb synset membership was kept, and so was noun synset membership where
    the file carries `noun_synsets` and `synset_nouns`. Synsets with a single
    member were dropped, because a synset of one relates nothing to anything.
  * Where the file carries `verb_forms`, irregular verb forms were kept,
    lower-cased and mapped to every base verb WordNet writes them under.
  * Glosses, examples, syntactic behaviours, sense keys, identifiers of
    dropped entries and all metadata other than the lexicon's own version were
    dropped.

Nothing was added and no entry was edited. The pruning is performed by
`build_lexicon.py` in the Qls toolkit's source, or by `qls-extract lexicon`,
which writes the same bytes; nothing else writes `lexicon.json`.

This NOTICE travels with the data. It is carried into the package that ships the
lexicon, and a build that shipped the file without it would leave undone the one
thing the licence asks for.
