Monolingual/Bilingual dictionaries

Cambridge Advanced Learner's Dictionary and Oxford Advanced Learner's Dictionary. You can use either of these two dictionaries (or both!) as your monolingual dictionary, for the whole of your degree. If you haven't started using them, it's high time you did. These are great tools that will help you complete vocabulary assignments successfully and solve general lexical doubts. But they can also be excellent tools when working on your writing assignments for other courses, and they can even help you solve pronunciation doubts!
CEF Levels: B2 to C2 (Upper Intermediate/Advanced)

Cambridge Dictionary of American English. Use this dictionary to learn about the differences between American and British English in terms of spelling, pronunciation, and word meaning and use, mainly.
CEF Levels: B1 to B2 (Intermediate/Upper Intermediate)

Cambridge Dictionary of Idioms. An idiom is a group of words which, when used together, has a different meaning from the one which the individual words that make it have. The English language is full of idioms (more than 15.000!), and native speakers use them all the time. In a nutshell, idioms should not slip your mind if you want to communicate successfully with other speakers of English!
CEF Levels: B2 to C2 (Upper Intermediate/Advanced)

Cambridge Dictionary of Phrasal Verbs. Phrasal verbs are an integral part of the English language. If you want to make your English sound more native-like, then you no doubt need to learn phrasal verbs. Remember: you must not only know what a phrasal verbs means but also, and most importantly, you must know how to use it.
CEF Levels: B2 to C2 (Upper Intermediate/Advanced)

Bilingual Dictionaries