Where can I find a glossary of odd terms and abbreviations in English sources? Some that were hard for me to decipher: AT, HMD, IPO? Thanks.It is not unusual for a reference book, especially those written from an academic standpoint, to have its own list of abbreviations or acronyms for standard sources. These usually appear at the beginning of the book. Unfortunately, these acronyms, especially short ones such as those given in the question, can have multiple meanings depending on the context. The online website, the Acronym Finder, lists 32 separate definitions for the acronym "HMD." This website also has an additional 83 definitions in the "Acronym Attic."
As I looked through this long list of meanings for "HMD" I saw several that could apply to the genealogical context. But that does not rule out the possibility that the acronym was a "one time" use for that particular reference book and does not appear in the list at all.
One book I like to use is the following:
Evans, Barbara Jean. A to Zax: A Comprehensive Dictionary for Genealogists & Historians. Alexandria, VA: Hearthside Press, 1995.
I find this book extremely useful to define truly old English and very archaic terms. Unfortunately, the acronym "HMD" does not appear in the book. But the acronym "H.M." applies to "his or her Majesty." Both "AT" and "IPO" have too many possible translations as to be virtually impossible to decipher. "AT" has 133 plus another 125 in the Attic of the Acronym Finder and "IPO" has 65 plus another 136.
The best strategy for this type of question is to look at the original reference book and search for the list of abbreviations or acronyms in either the front or the back of the book. As far as odd terms or archaic words are concerned, almost all of those words can be defined by a Google search. If you like to see them all in one place, look for a copy of the A to Zax book.