Use subject specific encyclopedias to gather background information and further familiarize yourself with a topic in a particular area of study. These specialized encyclopedias focus on your subject area and provide articles about topics in your field. Instead of trying to cover all knowledge, the coverage is very specific to your area of study. A good place to start if you need an overview and additional ideas for your research topic.
Use a subject specific dictionary for definitions of special terms unique to that area of study, or to learn how otherwise familiar terms are used to mean different things in that area of study. For example, take the word, journal. Depending on the context, a journal, may refer to a diary, various periodicals (i.e., academic journals), or to an accounting transaction in the double-entry bookkeeping system. A dictionary of Psychology will define terms as they are used in the area psychology.