Genealogists spend a great deal of time reading and extracting information from documents. Many times these documents are old and contain obsolete or unknown terms and unfamiliar abbreviations and acronyms. Deeds, wills and pension files are just of few of the records used by genealogists that are likely to have words that are not understood or can be misinterpreted by the reader.
Some words might not mean the same thing today that they meant 100 or 200 years ago. Other words have essentially been dropped from the English vocabulary.
I recommend that every genealogists have a few dictionaries to help interpret terms that they encounter during research. These dictionaries should cover the areas of medicine, law and historical terms.
Here are some suggestions:
A TO ZAX: A Comprehensive Dictionary for Genealogists & Historians (Alexandria, Virginia: Hearthside Press, 1995), by Barbara Jean Evans.
Abbreviations & Acronyms: A Guide for Family Historians, Revised 2nd Edition (Provo, Utah: Ancestry.com), by Kip Sperry.
Black's Law Dictionary: Definitions of the Terms and Phrases of American and English Jurisprudence, Ancient and Modern, Fourth Edition (St. Paul, Minnesota: West Publishing Co., 1968). This edition is the best for most genealogical work.
Colonial American English, a Glossary: Words and Phrases Found in Colonial Writing, Now Archaic, Obscure, Obsolete, or Whose Meanings Have Changed (Essex, Connecticut: Verbatim Book, 1985) by Richard M. Lederer, Jr.
Concise Genealogical Dictionary (Salt Lake City: Ancestry, 1989), compiled by Marine and Glen Harris.
A Medical Miscellany for Genealogists (Bowie, Maryland: Heritage Books, 2009), by Dr. Jeanette L. Jerger.
Nicknames Past and Present, 5th Edition (San Jose, California: CR Publications, 2007), Christine Rose.
Weights, Money and Other Measures Used By Our Ancestors (Baltimore: Genealogical Publishing Co., 1997) by Colin R. Chapman.
What Did They Mean By That? A Dictionary of Historical & Genealogical Terms Old & New (Westminster, Maryland: Heritage Books, 2000) by Paul Drake.
If the document is not in English, a translation dictionary is needed. An example that was created for genealogists is German-English Genealogical Dictionary (Baltimore: Genealogical Publishing Co., 1992), by Ernest Thode.
You may also need a medical dictionary which is contemporary to the time period of the document.
There also are Web sites that have information about old terms and abbreviations. A good list of these sites can be found on Cyndi's List under Dictionaries and Glossaries (http://www.cyndislist.com/diction.htm). Web sites for this purpose should be used with care. Check to see the source of the information. Goods sites will have a list of their sources on the page. If they are the books listed above, they should be fine. If no sources is listed, find a more reliable site.
Dictionaries will help you to better understand words and phrases found in old documents. It's not enough to just copy the words from a document into your files. It is essential to understand the meaning of all words and abbreviations used in a document in order to evaluate its value to your genealogical research.