sesquipedalian (n.) Look up sesquipedalian at Dictionary.com
1610s, "person or thing a foot and a half long," from Latin sesquipedalia "a foot-and-a-half long," from sesqui- "half as much again" (see sesqui-) + stem of pes "foot" (see foot (n.)). As an adjective 1650s.

Meaning "sesquipedalian word" (1830) is from Latin sesquipedalia verba "words a foot-and-a-half long," in Horace's "Ars Poetica" (97), nicely illustrating the thing he is criticizing.