In Ancient Greece they used the lovely word diaphanes. You can repeat it for its pleasure alone, not knowing what it means, but feeling how it fills the mouth with clear air and opens it to the sun with its double a. It has survived in English as diaphanous and is found in the Romance languages, as diafan in Romanian, and in French diaphane. In Romanian it refers to something light and delicate, like a feather or a spring dress; the French usage puts greater emphasis on admitting light: not entirely, but noticeably. Porcelain can be diaphane, or an autumn leaf, or parchment, the old or aristocratic skin on one’s hands. Broadening this meaning one can also use diaphane to describe a silhouette (“it was beautiful, elegant, and diaphane“) or even sunlight seen in a particular way (“The sun was clear and diaphane, like white wine.”) (Despite their delicacy, both quotes are drawn from Sartre.)

Marek Bieńczyk, Transparency. trans. Benjamin Paloff. Dalkey Archive Press, 2012 (2007)