This dictionary is for people who really want to master the Japanese language as well as native speakers.

If you are looking for a good mono lingual dictionary, I would like to recommend 「新明解国語辞典」。「広辞苑」might be more famous and standard dictionary for Japanese, but I don't think their definition of words are so clear . Besides, you won't find any joy of studying Japanese by the dictionary. 

But 「新明解国語辞典」is different. The definitions are simple and sometimes funny. For instance, you can check meaning of  「恋愛（れんあい)」 by the dictionary. If you can read the definition, you might find it interesting and feel intellectual satisfaction .

恋愛　れんあい
特定の異性に対して他の全てを犠牲にしても悔いないと思い込むような愛情をいだき、常に相手のことを思っては、二人だけでいたい、二人だけの世界を分かち合いたいと願い、それがかなえられたと言っては喜び、ちょっとでも疑念が生じれば不安になるといった状態に身をおくこと。