In NexisUni - all secondary sources are categorized in the Law Reviews and Journals filter from the Advanced Search.
Other law dictionaries include Ballentine's Law Dictionary (3rd edition) in Nexis Uni but no longer updated.
American Law Reports (a/k/a ALR) is a secondary source that contains brief articles (called annotations). ALR annotations cover specific topics that in great detail. Access is available through HathiTrust.
Legal encyclopedias are secondary sources that provide a general overview of almost every legal subject. The two major sets of U.S. legal encyclopedias are American Jurisprudence 2d (a/k/a AmJur) and Corpus Juris Secundum (a/k/a CJS).
Law reviews are considered the main forum for legal scholarship in the U.S. academic legal community.
Generally the articles included in these publications are written by law professors, judges, legal scholars, and law students. These articles contain a wealth of information, including footnotes that cite to primary authority and other secondary resources.