sesquipedalian

sesquipedalian \ses-kwuh-puh-DAYL-yuhn\, adjective:

1. Given to or characterized by the use of long words.
2. Long and ponderous; having many syllables.
3. A long word.

As a sesquipedalian stylist, he can throw a word like 'eponymous" into a sentence without missing a beat.
-- Campbell Patty, "The sand in the oyster", The Horn Book Magazine, May 15, 1996

Plus he has a weakness for what we can mischievously call sesquipedalian excess: Look out for such terms as "epiphenomenal," "diegetic" and "proprioceptive."
-- Jabari Asim, "Reel Pioneer", Washington Post, November 19, 2000

They walk and speak with disdain for common folk, and never miss a chance to belittle the crowd in sesquipedalian put-downs or to declare that their raucous and uncouth behavior calls for nothing less than a letter to the Times, to inform proper Englishmen of the deplorable state of manners in the Colonies.
-- William C. Martin, "Friday Night in the Coliseum", The Atlantic, March 1972

. . .her eccentric family's addiction to sesquipedalians (that big word for "big words"), and her furtive passion for flossy mail-order-catalog prose.
-- David Browne, "Books/The Week", Entertainment Weekly, October 23, 1998

Sesquipedalian comes from Latin sesquipedalis, "a foot and a half long, hence inordinately long," from sesqui, "one half more, half as much again" + pes, ped-, "a foot."