It seems to me that your objections to the use of the word "marmalade" for onions come from the fact that you give this word its English meaning, which is different from the "Latin" one.
In latin languages, a "marmalade" ("marmellata") does not necessarily require citrus rinds, but it's just opposed to the word "confiture" ("confettura") because of its homogeneous texture. On the other side, a "confiture" is supposed to contain solid fruit pieces.
So, you can't speak of an "onion marmalade", but you can speak of a "marmalade d'oignons" as well as a "confiture d'oignons".
In any case, the following recipe can be both an "Onion marmalade" and a "Confiture d'oignons"
CONFETTURA DI ARANCE E CIPOLLE
Ingredients:
-3 lbs oranges
-2 lbs red onions (if you were in Italy you should use the so-called "Cipolle di Tropea")
-1 2/3 lbs granulated sugar
-1/2 lb vinegar
-1 chili pepper (optional)
Soak the oranges in water for 3 days, changing the water daily. Half them and cut them in thin slices. Peel and slice the onions. Mix them together in a large pot, add the chili and cook them for 30-40 mins over a low heat. Add the sugar and vinegar and cook another hour. Cool down and serve with matured cheeses. Closed in a glass jar and refrigerated, lasts up to a month.
Pongi