Understandings around the nature of vocabulary knowledge and its relationship with vocabulary use in the productive domain remain vague. This study revisits the conceptualisation of vocabulary depth, its interplay with vocabulary size, and explores how both dimensions relate to productive lexical features in argumentative essays. Data on vocabulary knowledge were collected for 97 Chinese EFL learners in terms of form-meaning links, synonyms, collocations, and vocabulary size at four frequency levels, while data on productive vocabulary use were collected from their essays in terms of lexical diversity and lexical complexity indices. This research provides preliminary evidence for the organisation of vocabulary knowledge in the mental lexicon, as well as insights into its translation into productive vocabulary use.