Nominalization of Recondite

Solution 1:

The simple answer to your question is that there is no such word in current use (or at least in any dictionary I have checked.

you can always coin a word and, in doing so, there are potential rules about how to do it. For example, the word arcane is an English version of the Latin first declension adjective arcanus, of which the neuter plural is arcana. In Latin, it was (is, if you are in the Vatican City) normal to use a neuter plural of an adjective as the abstract noun. Thus arcana (literally arcane things is used as a virtual abstract noun.

The English adjective recondite is derived from the Latin verb recondo, meaning I hide, whose past passive participle (hidden or secret) is reconditus. So, if an ancient Roman writer had wanted a related word to refer to hidden things he would use recondita.

Your stab at a word is not bad. The only reason it is wrong is that the -ia ending is actually a third declension rather than a first declension ending. So the adjective memorabilis (from the adjective memor, meaning the quality of remembering), with the ending -abilis becomes capable of being remembered or memorable. And so we derive the English word memorabilia.

What you have to consider is whether, if you coin this word, your readers, or most of them, will understand it. Well, probably a majority of people reading a piece with a word like that in it will know the word recondite and make the short jump from there to recondita. But do you want to bring your reader up short in mid sentence in this way, or would it be better to find a more conventional way around it? This is an open question. If you decide to go ahead, however, there is a convention (call it good manners) to place a neologism in what are sometimes called 'scare quotes' to acknowledge that you are going outside standard English vocabulary.