dissertation vs symposium

dissertation

noun
  • A formal exposition of a subject, especially a research paper that students write in order to complete the requirements for a doctoral degree in the US and a non-doctoral degree in the UK; a thesis. 

  • A lengthy lecture on a subject; a treatise; a discourse; a sermon. 

symposium

noun
  • A collection of essays, articles or papers on a particular subject by a number of contributors. 

  • A drinking party in Ancient Greece, especially one with intellectual discussion. 

  • A conference or other meeting for discussion of a topic, especially one in which the participants make presentations. 

How often have the words dissertation and symposium occurred in a corpus of books? (source: Google Ngram Viewer )