To the excellent definition of Felipe Lorenzo del Río I only take the opportunity to add the original fragment of Quinto Horacio Flaco and some related links. The quote from Epistula ad Pisones ( "Epistle to the Pisones") or Ars poetica ( "Poetic Art") says « . . . proiicit ampullas et sesquipedalia verba . . . » ( " . . . leave the grandiloquence and the word standing and a half [long]. . . " ) and the recommendation is addressed to Telephus and Peleus. Other related voices are magnoverbophobia, megalogophobia, macrolexiphobia, macrolexiphilia, sesquipedaliophobia, cultiloquent, altiloquent, dolicologophobia.
The adjective derived from the latin, sesquipedalis, foot and a half long, very long. Horacio on the epistle rammers or poetic art uses the expression sesquipedalia verba: long words, a foot and a half, overblown and redundant words, archisilabos. The sesquipedalismo usually goes against clarity of language. From here it is derived sesquipedaliofobia or fear of long words, some are also called hipopotomonstrosesquipedaliofobia. If I didn't have broth, three cups.
