Exploring the etymology of "lacuna" involves taking a plunge into the pit-or maybe a leap into the "lacus" (that's the Latin word for "lake"). Latin speakers modified "lacus" into "lacuna," and used it to mean "pit," "cleft," or "pool." English speakers borrowed the term in the 17th century. It is usually pluralized as "lacunae," as in our example sentences, though "lacunas" is also an accepted variant plural. Another English word that traces its origin to "lacuna" is "lagoon," which came to us by way of Italian and French.