For research purposes, you will look for books that synthesize all the information on one topic to support a particular argument. Dictionaries contain lists of words in alphabetical order. The meanings of these words are given, as well as how they are pronounced. Some dictionaries may show how words are used in speech or writing and how the word came from other languages into our language. They also may trace the changes in the meaning of a word from the way it was used centuries ago to how it is now.
Encyclopedias provide material on almost any subject normally encountered.
They give summaries of all branches of knowledge. Encyclopedias provide a good beginning in our search for knowledge, but we should not stop with the information which we find in them. Subject encyclopedia contains in-depth entries focusing on one field of study. The articles in these are more detailed and are apt to be much more exhaustive than those in general encyclopedias. Gazeteers are dictionaries of geographical places.