Memorizing the dictionary is not the way you should study
English. It wouldn't help as the nobody has a "super
brain" who can memorize the entire dictionary. The best way to
improve your English is to read more books!...If you're frustrated
of reading books because it is too long or boring, try reading
newspapers and your vocabulary will gradually improve. Last but not
least, the most thrilling part of it is, you won't even realize
that you are improving (that's from my personal experience).
(remember to check the dictionary if you are unsure of the
defination of a word)