O Reitor dirige uma Universidade, enquanto o Diretor está restrito a uma Faculdade/Escola apenas. No Brasil, usa-se Reitor.

Em inglês, nem sempre a correspondência é biunívoca, pois o Reitor pode ser chamado de outros nomes, além de Dean (President, Chancellor, depende da universidade, do país, etc.).

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Note added at 24 mins (2005-05-08 16:28:59 GMT)
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Veja estes exemplos:

University of South Carolina Sumter Dean\'s Office
... DEAN OF THE UNIVERSITY. \"A university should be a place of light, of liberty, and of learning.\" -- Benjamin Disraeli. Les joined USC Sumter in 1993. ...
www.uscsumter.edu/dean/index.shtml

UTC | The University of Tennessee at Chattanooga
... A proven academic leader and native Tennessean will be the next Chancellor of The University of Tennessee at Chattanooga... ...
www.utc.edu/

Power Line
... Answering the call of the dominant newspaper of the Twin Cities, the president of the University of St. Thomas -- who had not himself attended the event ...
www.powerlineblog.com/

Mas, efetivamente, a palavra é dúbia, em inglês, podendo designar tanto o reitor como um diretor, além do que nós chamamos de \"vice-reitor para ...\" . Veja o que diz o Webster\'s:

dean (den)
n.
1 a) the presiding official of a cathedral or collegiate church b) R.C.Ch. a priest chosen by his bishop to supervise a number of parishes within the diocese
2 an official of a school, college, or university, esp. one in charge of students, faculty, or a division of studies
3 a) the senior member of a particular group b) an experienced and preeminent member of a group [the dean of American poets]
deanship
n.

Etymology
[ME den < OFr deien, dean < LL(Ec) decanus, chief of ten monks < LL(Ec), leader of ten < L decem, ten]

(C)1995 Zane Publishing, Inc. (C)1994, 1991, 1988 Simon & Schuster, Inc.