An ad eundem degree is a courtesy or honorary degree awarded by one university or college to an alumnus of another. The recipient of the ad eundem degree is often a faculty member at the institution which awards the degree.
Before modern transport had shrunk the world, it was common, when a graduate from one university moved into the neighborhood of another, for the new university to admit the graduate as a courtesy, "at the same degree" (in Latin, ad eundem gradum). Thus if someone was a bachelor of arts in the university that they had attended, they would likewise be a bachelor of arts of their new university. (Not every college extended this courtesy to all other colleges, however.)
The practice diminished in the early 19th century, but it continues at the Royal College of Surgeons in Ireland, the Royal College of Surgeons of England,, the University of Oxford, the University of Cambridge, and Trinity College, Dublin, where the process is known as "incorporation". It is an earned degree, not an honorary one, because it recognises formal learning. It is acceptable to list both the original degree(s) and the incorporated ("ad eundem") degree when listing post-nominals.
Several American universities, including Harvard,Yale,Brown,Penn, Dartmouth, and Wesleyan, follow a tradition that only alumni may be faculty (or sometimes that only alumni can be tenured faculty). Faculty who do not hold an earned degree are therefore awarded an honorary master's degree, often abbreviated M.A.H., ut in grege nostro numeretur ("so that (s)he may be numbered in our flock") as the degrees are described at Harvard. At Amherst College a similar custom is followed, with the granting of a Master of Arts degree by the college to its faculty even though the college grants only bachelor's degrees (AB) to its own matriculated students. Because these degrees do not involve any further study, most faculty members do not list them on their curricula vitae.