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. Another English word that traces its origin to "lacuna" is "lagoon," which came to us by way of Italian and French.
Derived forms of lacuna
In histology , a lacuna is a small space, containing an osteocyte in bone,  or chondrocyte in cartilage. The lacunae are situated between the lamellae , and consist of a number of oblong spaces. In an ordinary microscopic section, viewed by transmitted light, they appear as fusiform opaque spots.
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The critique extends into nearly every little crevice and lacuna of our civic life. Sometimes one cell is seen in each lacuna , sometimes shortly after cell-division a lacuna may contain two or more cells. And this lacuna has around it certain large round eminences which support the veins and arteries that ascend to the ventricle. This essay is an attempt to fill in a small part of the lacuna. There is evidently a lacuna , as the transition to Orestes is worse than abrupt.
Doublet of lagoon. Borrowed from Latin lacuna. Compare the inherited doublet laguna. First-declension noun. Compare the inherited lagoa and laguna.