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Can you give some examples of actual words with this element in them?
I tried every variant spelling I could imagine, in Latin and Greek, and couldn’t find any word that quite made sense.
Could “lagona(flask)” have something to do with that?
After looking around a bit, I think you must mean the suffix -lagnia, from the Greek word lagneia “lust”.
Here is a page I found with some -lagnia words.
I could only find this for the legnia in saprolegnia:
Saprolegnia (sapro-, “rotted” + -legnia, “border” – a “halo of rottenness”)
From: http://employees.csbsju.edu/wlamberts/bio306/vocab/vocab2.htm
The only l-word I know similar to “border” is Latin limen. It may be related somehow to this -legnia.