This is a great word, and means, literally, "a foot and a half long." It has come to be applied to people who use long words: words that are a foot and a half long.Dawguard said:sesquipidalian--a user of long words. Otherwise defined as someone who knows what it means. You are a sesquipidalian if you know what a sesquipidalian is.
(By the way, it's sesquipedalian)