It's different for everyone. It get in touch and a better understanding of how your own mind communicates with you I recommend the Genius Code Course.
Mastery is subjective. It depends on what you want from the dictionary. My own experience with dictionaries and reference books were eye opening as to what my mind is capable of and doing without me being aware of it. It lead me to understand that almost all learning is implicit. While we can watch, have some one explain the how to. It's only through actually doing the activity and testing my experience that I implicitly learn.
I have no need to master the dictionary myself. That's like me learning to bounce a soccer ball on my head when I have no interest in playing the game. Since you can read my answers my knowledge of the use of English words is satisfactory enough for my needs. I have as much mastery of the words in the dictionary as I need.
Alex
