It is a "portmanteau" (literally, "suitcase") word that's artificially carpentered together by combining Latin roots. "-iast" denotes a "practitioner," or sometimes a "performer"; an "enthusiast" is an emotional performer of his own excitement, and an an "ecdysiast," or stripper, is a "skin practitioner" or "-performer" (stripping was once called "the skin trade"). This suffix is common in portmanteau words. It's pronounced ek-DÍ-ze-ast.
"Ecce" is Latin for "I present to you"; Herod's "Ecce homo" concerning Jesus means "Here is the man." "Dentes," of course, are teeth; the coiner of the word (somewhat clumsily) renders "smile" as "a show of teeth."
Thus an eccedentesiast is someone who "performs by showing teeth," or smiling--a "professional smiler." The implication, naturally enough, is that such a person is insincere and merely putting on a show.
(Source: odzookers on Yahoo Answers)
Example:
The term "emotional labor" is like the word "eccedentesiast" (pronounced "ex-ced-den-tee-she-ist"): You might not have heard of it, but when someone tells you what it means, you recognize it instantly.
In fact, you might recognize yourself as an eccedentesiast -- someone who hides his or her true emotions behind a smile -- as well as someone burdened by "emotional labor," which is (at least in the context of nursing) the energy you expend to present that smiling face to patients, visitors, coworkers, and healthcare colleagues, regardless of how you are really feeling.(Source: Medscape Nurses > Viewpoints "When Nurses Need Nursing: The Toll of Emotional Labor" by Laura A. Stokowski, RN, May 13, 2014)
