No academic should ever give as a reference 'the Dictionary' - "It says in
the Dictionary that the word means ...";. Nor is it satisfactory academic proof of the existence or meaning of a word to say "It's in the Dictionary". There are many dictionaries, even in one language. Academics always say which Dictionary, and give the full details in a footnote or Bibliography.
An error not uncommonly seen is a reference in a student's work to the 'Oxford Dictionary'. There is, as far as AWE is aware, no such thing. The Oxford University Press (OUP) publishes a number of dictionaries, each one of which has a more precise name than the one above - The Concise Oxford Dictionary, for example - perhaps the commonest in use among students (one small volume); the Oxford English Dictionary, the most authoritative - and 20 very large volumes in length; and The Oxford Dictionary of English, a single volume aimed mostly at non-native speakers. In this, as in all referencing for academic work, be precise in copying the titles of the works you list.)