dean (n.)

early 14c., an ecclesiastical title, etymologically "head of a group of ten," from Old French deien (12c., Modern French doyen), from Late Latin decanus "head of a group of 10 monks in a monastery," from earlier secular meaning "commander of 10 soldiers" (which was extended to civil administrators in the late empire), from Greek dekanos, from deka "ten" (from PIE root *dekm- "ten"). It replaced Old English teoðingealdor.

Sense of "president of a faculty or department in a university" is by 1520s (in Anglo-Latin from late 13c.). Extended meaning "oldest member in length of service in any constituted body" is from mid-15c. Related: Deanery.

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Definitions of dean from WordNet
dean (n.)
an administrator in charge of a division of a university or college;
dean (n.)
a man who is the senior member of a group;
he is the dean of foreign correspondents
Synonyms: doyen
dean (n.)
(Roman Catholic Church) the head of the College of Cardinals;
Dean (n.)
United States film actor whose moody rebellious roles made him a cult figure (1931-1955);
Synonyms: James Dean / James Byron Dean