1650s, "having to do with prose," from Middle French prosaique and directly from Medieval Latin prosaicus "in prose" (16c.), from Latin prosa "prose" (see prose). Meaning "having the character of prose (in contrast to the feeling of poetry)" is by 1746; extended sense of "ordinary" is by 1813, both from French.
a prosaic and unimaginative essay
propulsion
propulsive
prorate
proration
prorogue
prosaic
proscenium
prosciutto
proscribe
proscription
proscriptive