I have used lot of dictionaries but at last I found a pearl in market in the form of Oxford advanced learners dictionary .At the starting page I realised the diffference between it and other dictionaries .It comes with rich vocabularies as wells as rich source of knowledge .The definition of each word and grammatical usage and word family is best of its contribution .Sometimes we fail to explain a particular word although we know it , at that time it helps us to come out of such trouble .I have been using it since few years and I do not feel need of any other dictionary while my studies .It comes with everything that a dictionary should maintain and provide .The most important feature of it is that it includes old english words which some times become necessary for reading poetry and prose .It is amazing dictionary .I really love this .