lexicon lexicon /ˈlɛksɪˌkɑːn/

noun

1. () A language user's knowledge of words  ( mental lexicon , vocab [Informal] , lexicon , vocabulary )
   a language user's knowledge of words
   
2. A reference book containing an alphabetical list of words with information about them  ( lexicon , dictionary )
   a reference book containing an alphabetical list of words with information about them
    If you don't know the meaning of a word, look it up in the dictionary
   If you don't know the meaning of a word, look it up in the dictionary