late 14c., from Old French prolixité "verbosity" (13c.), from Latin prolixitatem (nominative prolixitas), from prolixus (see prolix).
early 15c., from Old French prolixe (13c.) and directly from Latin prolixus "extended," literally "poured out," from pro- "forth" (see pro-) + base of liquere "to flow" (see liquid (adj.)).