https://medium.com/@prkrpubs/the-largest-vocabulary-in-hip-hop-myka-9-takes-the-crown-3f734b69e4ecI would not have guessed Mykah N9ne. I think he is up there, but that the sample size is too small. I am almost certain that MC Paul Barman and maybe MF DOOM have a larger vocabulary. There are also guys with less recorded or accesible material like Sesquipidelian and Divine Styler and Dose One. My Money is on MC Paul Barman, though:
https://www.youtube.com/watch?v=thABL7wiS0M 
