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.
(noun) - A long word.
"Poor Miss Matty got sadly puzzled with this, for the words gathered size like snow-balls, and towards the end of her letter, Miss Jenkyns used to become quite sesquipedalian." -- Elizabeth Cleghoen Gaskell, 'Cranford'
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."