The Latin sentence Lucus a non lucendo can be translated as "The word for grove is lucus because it is not light [non lucet] in a grove." This etymology by opposites is a byword for a notoriously far-fetched explanation of the derivation of a word.
It comes originally from the late 4th-century Roman grammarian Honoratus Maurus , "the most learned man of his time". Honoratus gives one more example of etymological explanation by opposites, "Bellum a nulla re bella", meaning "War is called bellum because there is nothing beautiful about it".
See also
References
Thilo, G. & Hagen, H. (eds) (1881). Maurus Servius Honoratus. In Vergilii carmina commentarii. (Leipzig). Available here.
